Nationwide Building Society is predicting a glut of mergers in the sector as the weaker players seek safety in the arms of a larger parent.
Unveiling record profits of £539m for the year, the chief executive, Philip Williamson, invited the small building societies to make him an offer.
"I know all the chief executives and I have said to them, 'if you get into trouble give me a call'," he said. "The phone isn't ringing yet," he added.
Nationwide is not planning any aggressive moves but it believes deals are inevitable before long.
There are 63 building societies and the assets of the other 62 are roughly equal to those of Nationwide, which is a giant in an industry of midgets.
"My gut feeling is that there will be further consolidation," Mr Williamson said. "But most societies are too small to be a particularly tasty morsel to a plc. It wouldn't be worth their effort."
Nationwide's profits rose 15 per cent despite a fall in its share of the mortgage market. Its share of new mortgage business stands at 6.7 per cent, compared to a traditional 9 per cent.
The fall was a result of Nationwide backing away from aggressive lending, fearing the heat of the housing market was leading some rivals to offer reckless deals to borrowers who might struggle to keep up with repayments.
Nationwide claims to have almost no bad debts. Of 1.2 million mortgage customers, only 69 are in arrears by three months or more.
The society, which is the fourth-biggest lender, is poised to start competing fiercely for new business once again and predicts a honeymoon period for mortgage borrowers.
Nationwide, the product of more than 100 mergers since it was formed in 1848, is now the second-biggest player in the savings market. Savings deposits grew by 23 per cent in the year to £8.3bn.
Nationwide has total assets of £120bn, making it easily the world's largest building society. It claims to have saved customers £690m in the past 12 months from the lower fees and better interest rates it is able to offer because it does not have shareholders to satisfy.
Nationwide has not faced any attempt to convert it into a bank for many years - a result, it claims, of having won the argument in favour of mutuality. It is attracting 3,000 new members a day.
The society is predicting a rise in house prices of between 3 and 6 per cent in the coming year, calming fears of a crash in the market.
Mr Williamson said he was sorry to see Standard Life, the only other remaining large mutual in the financial services sector, decide to convert to a plc. And he offered rare words of praise for Halifax, normally Nationwide's fiercest rival. He said: "Banks have started to learn some lessons. They realise that customers are important. HBOS is doing well - good on them. The good thing about us being big is that we are able to give the banks a run for their money."