Nationwide, the UK's biggest building society, says it is to merge with its smaller rivals the Derbyshire and Cheshire Building Societies.
Nationwide, the country's second-biggest provider of mortgages, said the tie-ups would create a mutually owned group with assets of £191 billion and £122 billion in retail deposits.
The mergers will be completed without a vote by the three societies' members, and Derbyshire and Cheshire customers will not receive a pay-out, Nationwide said.
Nationwide chief executive Graham Beale told reporters the mergers had not been initiated by the UK's Financial Services Authority in an effort to preserve market stability. The Derbyshire and Cheshire societies had both suffered bad debt-induced losses in the first half of 2008.
