Building society Nationwide is set to merge with rival Portman to create a mutual institution with total assets of over £150 billion (€220.318 billion).
Nationwide, the world's biggest building society, said the merger with Portman, third biggest in Britain, would give it a leading position in both mortgage and savings markets in Britain, winning it over 13 million members.
The merger is expected to become effective by the end of September 2007.
Nationwide's current group finance director, Graham Beale, will become chief executive of Nationwide next April, replacing Philip Williamson. He will then become chief executive of the enlarged group, which keeps the Nationwide name.
Portman members are expected to receive a minimum merger bonus of £200 million, representing a distribution of over 70 per cent of Portman's general reserves at the end of June.