Britain’s biggest accountancy firms are pushing to delay sweeping reforms to the industry, including a forced separation of their businesses, before parliamentary hearings this week.

The heads of Deloitte, KPMG, EY and PWC have written to the Commons business committee to say the competition watchdog should postpone moves to overhaul the audit market until the completion of a separate review by Donald Brydon, chairman of the London Stock Exchange, which could take another 12 months.

Mr Brydon was commissioned by Greg Clark, the business secretary, in December to investigate whether the work of auditors is good enough, but the review has not started.

Proposals by the Competition and Markets Authority include separating firms’ audit and consulting businesses as well as the biggest companies having to appoint two auditors instead of one.

The measures were a setback to the large accounting firms, which have lobbied hard against structural changes.

The heads of the Big Four auditors will be questioned by MPs tomorrow over a series of corporate failures, including BHS, Carillion and Patisserie Valerie. These have “highlighted glaring weaknesses in audit”, according to Rachel Reeves, chairwoman of the committee, who is leading a parliamentary inquiry into concerns about the accountancy industry.

The written submissions to Ms Reeves’ inquiry have raised concerns that the Big Four firms want to push back on what would be the biggest changes in a generation.

Prem Sikka, professor of accounting at the University of Sheffield, said: “The CMA’s reforms must not be postponed as audit quality and the audit market is in a dire state. The proposed reforms are mainly about competition and choice and are not dependent on a debate about the nature and purpose of audit.”

Tim Bush, head of governance at the shareholder advisory group Pirc, said he was concerned that the Big Four firms were trying to “kick the can down the road”, adding: “I think [the Big Four are] hoping the Brydon review changes the destination of the road.”

In Deloitte’s submission to Ms Reeves, David Sproul, chief executive, said: “The Brydon review will be of fundamental importance and its findings should be understood and considered in advance of any final decisions on reforms to the structure of the audit market.”