The Financial Services Authority has approved a merger bid for the Chesham and Skipton Building Societies.
Over 80% of Chesham's customers voted in favour of the move to combine with the Skipton Building Society, in a yearly meeting which took place in April.
Chesham is the longest surviving building society in Britain, and was founded in 1845. It is expected to marry up with the Yorkshire-based Skipton on 1 June.
Chesham's members will be able to use Skipton's 92 branches spread across the UK from 1 June onwards.
Skipton's plans involve retaining the Chesham branches for one year before reviewing the business.
Chesham chief executive Paul Kilbride is pleased that the society's customers are happy for the deal to go ahead, as is Skipton chief executive David Cutter.
Skipton is also set to launch a new product - the 95% LTV mortgage for first time buyers, along with a range of 90% LTV products for introducers with the Skipton divisions Connells and Pink Home Loans.
