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Governed AI for UK accountancy practices

AI does the casting. You do the ruling.

Cast & Rule does your routine work on private hardware in your practice, built around your own workflows and run under your firm's rules. Always under human guidance.

Nothing goes to a client or HMRC until you've ruled it off.

Take the product tourDiscuss a scoped pilot

Hollin & Vey LLP

For ruling

03 proposed workpapersHeld in the practice

  1. Management pack

    Linden & Moss Architects LLP

    Quarterly figures assembled for review.

    WP / 026 · 4 source documents
    Checks complete

  2. Chase email

    Rowe Garden Design

    A draft request for outstanding records.

    WP / 027 · Draft only
    Checks complete

  3. Advisory note

    Skelwith Joinery Ltd

    Cash-flow observations from the quarter's figures.

    WP / 028 · Sources attached
    Checks complete
Anna Bennett FCAPartner
Awaiting partnerPartner sign-off

What it means for your practice

The speed of AI, without losing control

Staff in many practices already use AI. The questions are whether you set the rules, whether you can prove what left the building, and whether you can show which work was the AI's and which was yours.

  1. Runs on hardware in your practice

    ICAEW says confidential client data mustn't go into public AI tools. A policy nobody can enforce doesn't close that gap.

    Cast & Rule runs on hardware in your practice, so with cloud AI switched off no client data leaves the building, and a report you can check shows what did leave through Cast & Rule.

  2. A partner decides what goes out

    Work that leaves under your firm's name is your responsibility, however it was prepared.

    The machine's work stops once it's prepared. Cast & Rule holds it there for a named partner's decision.

  3. You can show which work was whose

    If a client, insurer or regulator asks what the AI did, someone at your practice needs to be able to answer.

    The Ledger records what the AI did and what your people did, with the task, its version and the model used, so you can show which work was whose.

  4. Less time on routine prep

    Management packs, advisory drafts and client chasing still eat into partners' and seniors' evenings.

    Cast & Rule drafts that work from each client's own records, to your templates and your timetable.

The problem

AI is already in accountancy work. Where does it run in your practice?

Surveys of office workers find staff using AI tools their employers haven't approved, and some typing in customer data. ICAEW's guidance on generative AI says confidential client data mustn't go into public tools. Its July 2026 reminder on confidentiality (Code section 114) applies inside the firm too.

A policy that nobody can enforce doesn't close the gap.

Shadow AI

People are taking up AI faster than their firms. Karbon's January 2026 report, from nearly 600 accounting professionals, found that 98% of firms now use AI and 83% of respondents report growing awareness of data security.

MTD for Income Tax

Quarterly updates became compulsory on 6 April 2026 for sole traders and landlords with qualifying income over £50,000. The threshold falls to £30,000 in April 2027 and £20,000 in April 2028.

Hand-built work

Management packs, advisory drafts and chasing for documents still eat into partners' and seniors' evenings.

  • of accounting firms now use AI (nearly 600 professionals surveyed)

    Karbon, State of AI in Accounting 2026

  • of respondents report growing awareness of data security

    Karbon, State of AI in Accounting 2026

  • MTD for Income Tax threshold from April 2027, down from £50,000

    GOV.UK: Making Tax Digital for Income Tax

Cast & Rule gives your team a safe place to use AI: on local hardware your practice controls, under your rules, with a record of what the AI did.

A policy is where it starts. Get the policy template

One product, eight parts

Named in your practice's own language

It's organised the way a practice already works. The machine prepares, your rules check, and a partner decides.

01

Prepare

Drafts from each client's own records, to your templates and your timetable.

Workpaper · MTD quarterly update

Client
Hollis Joinery
Source
Xero export · imported 09:10
Schedule
Quarterly · due 7 Nov

  • Workpapers

    Working-paper templates the Clerk drafts from: MTD quarterly update, management pack, engagement letter.

  • Schedules

    Jobs that run to a timetable: the MTD tracker for each client, and the chasing that goes with it.

  • Sources

    Read-only connections to the client's records: Xero, Microsoft 365, Companies House and HMRC.

02

Check

Your firm's rules limit what each task may do. Client files are processed on local hardware you control, and what the AI did is posted to the Ledger.

Rules · this workpaper

Processed on the practice's own hardware
Passed
Figures reconcile to the source
Passed
Nothing is sent without a partner
Held

  • Rules

    Your firm's AI-use policy, applied as permissions on each task rather than filed as a PDF.

  • The Strongroom

    Keeps each client's records in its own locked compartment, on local hardware the practice controls.

  • The Ledger

    The practice's record of what the AI did: who did what, and when. Each entry is locked to the one before it, so a later change to a checked entry shows up.

03

Review

You see what needs a decision, with the evidence beside it, and rule it off.

For ruling · A. Bennett FCA

Hollis Joinery · MTD Q2
0 exceptions
Pellow Bakery · management pack
1 query

  • The Desk

    Where the partner works: what needs your decision, deadlines coming up and recent work, in one place.

  • Ruling

    The partner sign-off queue: client, period, who prepared it, what was flagged and how long it has waited, with the evidence beside it.

See how each part works

Where it helps first

MTD quarters and advisory packs

MTD for Income Tax, client by client

Schedules shows each client's quarterly update and the chasing that goes with it. Updates are prepared from the client's records, then wait for review. You keep submitting through your MTD-recognised software.

  • Each client's quarter at a glance
  • Reminders when records are missing
  • Updates wait for the partner

Cast & Rule builds against HMRC's MTD interfaces. Getting ahead on MTD

Advisory and management packs

Workpapers drafts first versions from the client's ledger figures, in your house style, with each figure that matters linked to its source. You edit, then rule it off.

  • A first draft from the client's own figures
  • Your firm's structure and tone
  • Drafts and edits recorded in the Ledger

Working together

We build AI around how your practice works

Cast & Rule is a product, and a partnership. We learn how your practice runs, build the automations around your clients and your way of working, and keep adding to them over time.

However far it grows, three things don't change: your rules decide what may run, a named partner rules on what goes to a client or HMRC, and the Ledger keeps the record.

How we work together

  1. We learn how you work

    We sit with your team and map the work that takes the most time: your templates, your client mix and how you review.

  2. We build for your practice

    We turn that work into tasks that run your way, with your templates, your house style and your checks, for your clients.

  3. We add one workflow at a time

    Once a workflow is accepted, we move to the next. Each new one is prepared by the machine and waits for a partner.

  4. We review it with you, regularly

    We meet on a schedule we agree together to look at what's working, what the Ledger shows and what to build next.

The daily work, in view

Small tasks. A clearer day.

See what is due, what is missing and what is ready to consider. Four views of the work, inside the same practice boundary.

Explore the practice workflows
Hollin & Vey LLP / Workpapers
01 / Locate

MTD deadline radar

A quarter’s work, held in one view.

Read as a list
  • A quarter drawn as a line from Quarter opens to Review to Due.
  • Four clients are plotted along it by how far their work has reached.
4 clientsthis quarter
02 / Gather

Client chasing

Missing records become a clear request.

Read as a list
  • Invoices, Bank feed, Receipts each lead to the Draft chase.
1 draftheld for partner review
03 / Prepare

Advisory drafting

An observation, with its working attached.

Read as a list
  • Working paper and Client notes lead to the Cash-flow observation.
  • Cash-flow observation is marked: Draft · not advice.
2 sourcesalongside the draft note
04 / Be found

AI-answer visibility

A practice description that can be cited.

Accountants for a growing practice?
Hollin & Vey LLPPractice services · source page

Example answer and citation only

1 citationin an AI answer

Hours estimator

Put in your own workload and assumptions and see a monthly figure, before and after the checking that comes with it.

Estimate your hours

Trust

Built for a profession that runs on evidence

Client files are processed on local hardware in your practice. Your firm's rules decide what may run. The Ledger records what the AI did. The security pages set out each control in full, for partners, practice managers and IT leads.

Written to be checked, not taken on trust.

Read the security overview

Connections

Brings your clients' records into one workflow: read-only first, and one client per connection. Work also starts from an export you supply.

Choose a connection to see what it does. On a keyboard, use the left and right arrow keys.

HMRC Making Tax Digital

Cast & Rule prepares the quarterly update for a partner to review. Your practice submits it through its existing MTD-recognised software.

Companies House

Reads public filing data (confirmation statement and accounts due dates, and filing history) to feed your deadline tracker. It uses public-register data only, and makes no filings.

Xero

The first connection. Read-only access to one Xero organisation per connection, through Xero's official interface. Any write, such as posting or adjusting entries, needs a partner's ruling on that exact action. Xero's own app terms and connection limits apply.

Microsoft 365

Read-only access to mail, calendar and files through Microsoft Graph, Microsoft's official interface, limited to what each task needs.

Dext

Receipts and invoices your clients capture in Dext, read-only, one client per connection.

Supported exports

Many practice systems export records, including ones with no public interface. The pilot starts from exports you supply, in the formats your software already produces.

1 of 6

Read as a list

All 6 connections lead into your practice: read-only, one client per connection.

HMRC Making Tax Digital
Cast & Rule prepares the quarterly update for a partner to review. Your practice submits it through its existing MTD-recognised software.
Companies House
Reads public filing data (confirmation statement and accounts due dates, and filing history) to feed your deadline tracker. It uses public-register data only, and makes no filings.
Xero
The first connection. Read-only access to one Xero organisation per connection, through Xero's official interface. Any write, such as posting or adjusting entries, needs a partner's ruling on that exact action. Xero's own app terms and connection limits apply.
Microsoft 365
Read-only access to mail, calendar and files through Microsoft Graph, Microsoft's official interface, limited to what each task needs.
Dext
Receipts and invoices your clients capture in Dext, read-only, one client per connection.
Supported exports
Many practice systems export records, including ones with no public interface. The pilot starts from exports you supply, in the formats your software already produces.

See all connections

Built on request

We build a connector to your own systems

If your practice relies on a system that isn't shown here, we can build a custom connector to it on request, so Cast & Rule fits the tools you already use. It follows the same rules as every other connection: it reads first, it's tied to one client, and a partner rules on any action that would change that system.

Ask about a connector

This works where the system offers an API or an MCP server (a standard way for AI tools to connect) that we can be given access to.

One practice first

Start with one workflow, over six weeks, with us alongside

For a UK practice of 5 to 20 staff, with a partner who'll own the review. We run one workflow, measure it before and after, and agree in writing how it ends. Send an enquiry or email us today.

Discuss a scoped pilotor take the product tour firstenquiries@castandrule.example

Questions partners ask

Frequently asked questions

Is Cast & Rule an accountancy firm?

No. Your firm keeps the client relationship, the professional judgement, the tax treatment and the sign-off. Cast & Rule builds and runs the systems that support that work, alongside the ledger and practice software you already use.

Can our staff send client data to a cloud AI through Cast & Rule?

Cast & Rule sends work to a cloud model only when your firm's rules allow it for that task and that person, after names and tax references are swapped for placeholders on your own machine. Tools outside Cast & Rule, such as a browser on a staff laptop, stay under your own policy and IT settings, and our AI-use policy template helps with those.

Can we prove nothing left the building?

Yes. For any period, the no-cloud report lists every AI run, where it ran and what left the machine through Cast & Rule, and you check it without asking us. With cloud AI switched off, it shows no cloud calls at all.

Who controls what the AI is told to do?

Your firm decides what may run and for whom. The tasks themselves are built, signed and versioned by us, so neither your staff nor anyone else can quietly change what the AI is told to do; your practice adjusts only the settings we allow, and each change is recorded. We found no competitor offering tasks that are maintained centrally and extended for each firm (as of September 2026).

What happens when an AI model changes or is withdrawn?

Nothing changes without you. Each task is tested against named model versions, and a new version installs only after you've tried it on your own machine and approved it. If a cloud model is withdrawn, the task carries on with the tested model on your hardware. We found no competitor offering upgrades that you test on your own machine and that install only when you approve them (as of September 2026).

Could one client's information turn up in another client's work?

No. Each client's records sit in their own encrypted store, with their own key, and each piece of work reads from one client only. Delete a client's key, including its backed-up copies, and their store can no longer be read.

Can we tell what the AI did from what our people did?

Yes. The Ledger marks every change as made by a person or by the AI, with the task, its version, the model and the documents it changed. Each entry is locked to the one before it, so a later change shows up.

Who signs the work off?

A named partner. The machine's work ends once it's prepared, and Cast & Rule holds it there until a partner rules on it.

How do we start?

With a six-week pilot of one workflow at your practice, supervised and measured before and after, with a written exit.

Contact us