"Nationwide Building Society today announces that it will merge with The Derbyshire Building Society and The Cheshire Building Society, who will transfer into the Nationwide Group by way of two separate transactions," it said in a statement.

All three groups are building societies, meaning they are owned entirely by their members, or customers depositing money with them.

"The Derbyshire and The Cheshire have independently concluded that a merger with Nationwide is in the best interests of their savers and borrowers given the financial issues faced by both societies," Nationwide's chief executive Graham Beale said in the statement.

The enlarged group would have assets totalling more than 191 billion pounds (237 billion euros, 337 billion dollars) and retail deposits of 122 billion pounds, Nationwide said.

The terms of the transactions were not given.