New-York-based firms Warburg Pincus LLC and tabled ajoint bid valued at about £400 million for U.K.-based challenger bank CharterCourt Financial Services, Sky News reported April 8, citing sources.

It was reported in January that U.S. private equity firmElliott Associates, which owns a controlling stake, had put Charter Court upfor sale.

A source said that some bidders are using new buy-to-letmortgage underwriting standards proposedby the U.K. Prudential Regulation Authority to try to push down the price tag.Charter Court generates a significant amount of revenue from buy-to-let.

BC Partners and General Atlantic Partners have alsoreportedly made bids for the firm, Sky News reported.

Charter Court Financial Services is a trading name ofCharter Court Financial ServicesLtd, which also owns a savings bank business.