Staffordshire Building Society says it is attracting disgruntled members of Birmingham Midshires who did not vote for the Halifax take over.
Staffordshire is now the sole building society based in Wolverhampton.
It says Birmingham Midshires members are voting with their feet because they want the better treatment and deals building societies offer.
Staffordshire chief executive Keith Page says: "I would like to thank Halifax and the board of Birmingham Midshires for the wonderful opportunity they have provided.
"As a local building society we are looking forward to welcoming the customers of the Birmingham Midshires who would prefer to be with a building society rather than a bank."