The Portman Building Society was a UK mutual building society, providing mortgages and savings accounts to UK consumers and offering loans to commercial enterprises. Its head office was located in Bournemouth and its administration centre in Wolverhampton. Portman merged with the Nationwide Building Society in August 2007, at which time it was the third largest building society in the UK and the largest regional building society in the south of England, with 154 branches and assets exceeding £15 billion.