Accountants PII limit sizing: going above the ICAEW compulsory minimum

~4 min read

Reviewed by Matthew Bartlett, Director · Last reviewed 2026-07-06

The Professional Indemnity Insurance Regulations made under ICAEW Bye-law 61 set a compulsory minimum PII limit for every firm in public practice — the greater of £1.5 million or 2.5 times gross fee income for the last completed financial year. That figure is a compliance floor. For most firms of any real size, the compulsory minimum is well below the realistic exposure on any given engagement, and prudent placement means sizing above the floor. This entry walks through how a broker actually approaches the sizing exercise on the accountants side, the factors that push the recommendation up or down, and how the layers are typically structured.

The factors that drive the recommendation up

Four factors tend to move the recommendation materially above the compulsory floor. The first is engagement value. A firm handling a single audit engagement worth £250,000 in annual fees, on a client with a balance sheet in the £100 million range, faces claim exposure that could dwarf 2.5× the firm's overall fees. The second is client concentration — a firm where a single client represents more than 20 per cent of fee income carries structural exposure that a lower-concentration book does not, because the loss of that client to a mismanaged engagement can cascade beyond the single claim into partnership stability issues. The third is service line. Corporate finance advisory, complex tax planning, valuations for M&A transactions, and expert witness work each carry claim severity distributions that skew materially higher than routine audit or bookkeeping. The fourth is claims history — a firm with a paid claim in the last six years, or an open reserve, sits differently in an insurer's eyes and should typically carry more limit rather than less.

The factors that push it down

Two factors push against sizing well above the floor. The first is cost: additional layers cost money, and beyond a certain point the marginal risk-reduction from another £5 million of limit is modest against the marginal premium. The second is insurer appetite — the accountants' primary market has a smaller pool of insurers than the wider commercial market, and stacking layers requires the second and third insurers to be willing to sit above the primary at a rateable price. Where appetite for a top-up layer is thin, the primary insurer can sometimes increase its own limit rather than involve a second insurer, but the pricing is not always favourable.

The sizing exercise, step by step

A structured sizing exercise looks at four things in sequence. First, identify the compulsory minimum from the 2.5× formula and set it as the operative floor. Second, identify the largest single realistic loss the current book of work could generate — this is not a theoretical worst case but a considered look at the largest live engagement, the largest transactional matter, and the highest-severity client. Third, review the last six years of claims and notified circumstances to see whether the historical severity distribution supports or challenges the "largest single realistic loss" figure. Fourth, decide the primary layer size to sit meaningfully above that figure, and consider whether a top-up layer above the primary makes sense.

Layer structure

Most accountancy practices at scale carry a two-layer tower. The primary layer sits at or above the ICAEW compulsory minimum, typically written by one of the panel accountants' PI insurers. The top-up layer sits above the primary and is often placed with a different insurer for spread and capacity reasons. Aggregation on the top-up wording is usually harmonised with the primary — insurers do not like a top-up that would drop into an engagement while the primary was disputing an aggregated series of losses.

Worked examples

Illustrative only. Three sketches:

Sole practitioner tax adviser, £180,000 fees, largest client £22,000 fee. Compulsory minimum £1.5m (floor). No individual engagement above £22,000 in fee. Sizing recommendation: £1.5m primary, no top-up. Historical claims record clean.

Six-partner mixed practice, £2.4m fees, one FTSE-listed audit worth £180,000. Compulsory minimum £6m (2.5×). Largest realistic loss on the FTSE audit — say £8-15m depending on the mis-audit scenario. Sizing recommendation: £6m primary + £4m top-up = £10m tower.

Twelve-partner audit-heavy firm, £8m fees, four listed clients. Compulsory minimum £20m (2.5×). Largest realistic loss on any one of the four listed audits — potentially into eight figures. Sizing recommendation: £15m primary + £15m top-up = £30m tower, subject to insurer appetite on the top-up.

What not to do

Two failures recur. The first is carrying the compulsory floor as a target rather than a minimum — a firm sizing at £1.5m because that is the ICAEW floor, while running a book that carries a realistic single-loss exposure of £5m, is under-insured on its own book. The second is placing the top-up with the same insurer as the primary in the belief that consolidation is efficient. It is efficient administratively, and it is inefficient risk-wise, because a claim that erodes the primary erodes the top-up in the same policy year with the same insurer's appetite.