The rules
Buying an accountancy firm: the audit control rules, with sources
Updated
Four rules a buyer of a firm with an audit arm meets, each read from the legislation's or ICAEW's own page on 28 October 2026.
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The rules, one by one
Controller of a corporate member: 15% of the votes
In sub-paragraph (2)(b) and (c) “controller”, in relation to a body corporate, means a person who either alone or with an associate or associates is entitled to exercise or control the exercise of 15% or more of the rights to vote on all, or substantially all, matters at general meetings. (read 28 October 2026)
Source: Companies Act 2006, Schedule 10 Part 2
Majority stake, and the higher thresholds some firms set
While a majority stake is more than 50%, some audit firms may have clauses in their governance arrangements that specify higher thresholds, in some cases as much as 75% or even 100%. (read 28 October 2026)
Source: ICAEW: what private equity might mean for a firm's audit status
A non-accountant holding 10% needs ICAEW approval
ICAEW asks a firm to ensure all non-authorised persons holding a material interest have been approved by ICAEW, and this includes a person holding at least 10% of the shares in a body. (read 28 October 2026)
Source: ICAEW: eligibility when changing your firm structure
ICAEW's application time: 8 to 12 weeks
Please allow 8-12 weeks from the date the Regulatory Support team has obtained all of the required application information and has passed your application to the case manager team. (read 28 October 2026)
Source: ICAEW: eligibility when changing your firm structure
Where the rest of the rules sit
ICAEW, as a recognised supervisory body, publishes its own guidance on private equity investment in audit firms, and its 2024 regulatory news sets out the definitions of majority and voting rights it applies. The FRC's Ethical Standard is the independence standard an audit firm applies whoever owns it. None of these pages states a figure of its own, so they are linked here rather than tabled.
Source: ICAEW (RSB): private equity investment in audit firms
The key definitions ICAEW applies to majority and voting rights are on its own page.
Source: ICAEW: audit eligibility changes, key definitions
The FRC's Ethical Standard for auditors.