CIOT and ATT tax specialist PII: what tax advisers need to know

Reviewed by Apex Insurance Brokers · Last reviewed 2026-07-06

In short: Under the CIOT and ATT Compulsory Professional Indemnity Insurance Regulations, in force since 1 January 2023, a member in practice must make sure their firm holds at least £1 million of cover for each and every claim. If the firm’s gross fee income is under £400,000, the minimum is the greater of 2.5 times gross fee income and £100,000. The excess may not exceed £30,000 per principal, and cover must stay in place for at least six years after the member stops practising. If the firm is also regulated by ICAEW, ICAS or ACCA, the policy must meet both sets of rules.

Two professional bodies regulate the specialist end of the UK tax profession: the Chartered Institute of Taxation (CIOT) and the Association of Taxation Technicians (ATT). Both operate their own Professional Rules and Practice Guidelines, and both require members in practice to hold professional indemnity insurance cover. Tax advisers who also hold accountancy credentials — commonly ACCA, ICAEW or ACAScot — are simultaneously bound by their accountancy body's PII regime, and the effective requirement is the more demanding of the two. This entry sets out what the CIOT and ATT rules require, how they compare to the accountancy regimes, and what tax-specialist firms should look for at renewal.

The CIOT rules

Every CIOT member in practice must make sure their firm holds professional indemnity insurance that meets the joint CIOT and ATT Compulsory Professional Indemnity Insurance Regulations, in force since 1 January 2023. The minimum is £1 million for each and every claim, or, if the firm’s gross fee income is under £400,000, the greater of 2.5 times gross fee income and £100,000. The policy must cover all civil liability, including costs and expenses, arising from taxation services, and the excess may not exceed £30,000 per principal.

Firms undertaking specialist tax investigation work, complex international tax planning, transfer pricing, or R&D tax credit advisory should read the CIOT guidance as recommending significantly higher limits than the base position. HMRC enquiry claims and appeals can generate loss claim quanta well above the fee generated on the underlying engagement, particularly where a mis-planned position exposes the client to a tax liability plus interest plus penalties.

The ATT rules

ATT members in practice are covered by the same joint regulations, so the same minimums apply: £1 million for each and every claim, or the greater of 2.5 times gross fee income and £100,000 below £400,000 of fees. ATT's core membership is technicians rather than chartered advisers, which typically means a smaller practice profile and a lower average engagement size. ATT-only firms that grow into higher-value tax planning work should treat the compulsory minimum as a floor and size upward as the profile of work moves up-market.

Dual-regulation with accountancy bodies

A large proportion of CIOT and ATT members also hold ACCA or ICAEW credentials, and many firms operate under both hats. Where that is the case, the firm's PII cover must satisfy both regimes. In practice, the accountancy body's rules are usually the more demanding: for the same fee income, ICAEW’s minimum (£2 million, or 2.5 times fees with a £250,000 floor below £800,000) is never lower than the CIOT/ATT minimum. Check the basis, though. CIOT and ATT require the minimum for each and every claim, while ICAEW allows an aggregate limit, so the policy must meet both tests.

Firms operating solely under CIOT or ATT credentials, without an accountancy body layer, need to be careful that the placed policy meets the CIOT or ATT wording expectations. In particular, defence costs handling and the scope of the "professional business" definition should be checked, because CIOT/ATT rules are less prescriptive than the ICAEW Regulations and it is possible to place a policy that would be non-compliant for an ICAEW firm but is acceptable for a CIOT-only firm — creating a wording gap if the practice later takes on ICAEW-regulated staff.

Tax investigation work

Tax investigation work — representing a client under HMRC enquiry, an appeal to the First-tier Tribunal (Tax), or a settlement negotiation — carries a claim severity profile that a general adviser's PI wording does not always contemplate. Wordings that limit cover to "civil liability" without expressly extending to fee disputes with HMRC, tribunal costs recovery, or interest and penalty exposure can produce coverage gaps in exactly the scenarios tax specialists most need cover. Any tax-focused practice should review the wording specifically for tax-enquiry cover at every renewal.

Run-off

Both CIOT and ATT require professional indemnity cover to stay in place for at least six years after a member stops practising (regulation 7.1), unless the buyer of the firm has agreed in writing to provide it (regulation 7.2). For a tax-planning practice with material historical advisory work, longer cover may be worth considering, given the HMRC discovery assessment window and the possibility of enquiries opening several years after the tax year in question.

Worked example

Illustrative only. A two-partner boutique tax practice. Partner A is CTA (CIOT Fellow) and ACA (ICAEW). Partner B is ATT-only. Fee income £550,000, mainly personal tax planning and HMRC enquiry work. Under ICAEW: minimum £1,375,000 (2.5 × £550,000) for any one claim and in the aggregate. Under CIOT and ATT: £1m for each and every claim, because fees are over £400,000. Operative minimum: £1,375,000, driven by the ICAEW regime, on a basis that also gives £1m for each and every claim. Broker recommendation given the tax-enquiry focus of the book: £3m primary layer with an explicit endorsement covering HMRC investigation work and interest/penalties exposure, six-year run-off (the CIOT/ATT minimum) costed alongside the active policy so the partners can decide at cessation whether to extend.