The investment values London-based CFC at more than 2.5 billion pounds ($3.45 billion), representing a multiple of 40 times earnings before interest, taxes, depreciation and amortisation (EBITDA), a source familiar with the matter told Reuters.

CFC, founded in 1999, offers business insurance cover for areas such as cyber, environmental liability and medical malpractice, and has 100,000 customers.

Demand for cyber insurance has risen as ransomware attacks have escalated in the past couple of years.

"Cyber is a huge growing area," said CFC CEO Graeme Newman.

"We are only scratching the surface in SME businesses."

The investment will enable CFC to build on its existing strategy, including investment in technology and increasing headcount, CFC founder and group CEO Dave Walsh said.

Vitruvian was a reinvestor in the firm, and EQT was a new investor, CFC and the two firms said in a statement.

The number of employee shareholders will rise to more than 300 from 175 following the deal, with employees remaining the largest shareholding block in CFC. CFC currently has 500 staff.

Evercore advised CFC, while EQT was advised by Morgan Stanley, Kirkland & Ellis, KPMG and Bain & Company, the source added.

($1 = 0.7245 pounds)

(Reporting by Carolyn Cohn in London and Muvija M in Bengaluru; editing by Anil D'Silva and Jason Neely)