Bradford & Bingley Building Society members have voted in favour of a resolution to convert to a bank.
A motion in favour of demutualisation was supported by 62 per cent of those voting.
The turnout for the election, held over the last six weeks, was 63 per cent of the society's 2.9 million members.
Building Societies Association director general Adrian Coles says: "It is disappointing that our members have succumbed to the lure of a quick buck.
"Building society reserves have been built up by our parents, grandparents and great grandparents and should be held in trust by today's generation to benefit tomorrow's."