John Connolly, who was chief executive of Deloitte UK, is said to be plotting a string of acquisitions to take on his former employer along with EY, PricewaterhouseCoopers and KPMG.
He is working on the project with private equity house HG Capital.
Sources told Sky News that Blick Rothenberg, a London-based accountancy firm taken over by HG last month, will be rebranded Cogital Group under the scheme.
Filings at Companies House show that Connolly and HG have established Cogital Group. The former Deloitte chief is to be chairman of the company.
Founded in 1945, Blick Rothenberg currently has 28 partners and directors and employs more than 200 people.
In comparison, PwC claims a total global workforce of more than 200,000, with around 20,000 in the UK.
HG Capital and Blick Rothenberg declined to comment.
Announcing its investment in Blick Rothenberg last month, HG Capital did not disclose the “terms of this transaction”.