Bosses at the Bradford-based Yorkshire Building Society have signed up to a nationwide branch-sharing scheme with rivals Britannia.
The initiative will mean customers of both mutual societies can use more than 300 shared branches across the country.
Both companies were quick to stress the move was not a step towards branch closures or a merger but simply a cost effective way of improving services.
Work is already underway on developing the necessary computer systems to accommodate the changes and the agreement should take effect early next year.
Britannia's 2.2 million members - which make it the UK's second largest building society - will be able to pay into and withdraw money from Yorkshire's 132 outlets free of charge. Likewise, the Yorkshire's 1.8 million members can take advantage of Britannia's 190-strong network.
Yorkshire's chief executive David Anderson said: "Yorkshire and Britannia are both committed to offering their members the best possible service and sharing our branch network is a practical way of enhancing the benefits we offer."
Graham Stow, chief executive of Staffordshire-based Britannia, said: "At a stroke we will expand our network without adding to our costs, providing real added value to our members."
Mr Anderson stressed both societies planned to remain independent and there were no plans for a future merger. However, they would look at ways of working together to improve services further, he said.
Mr Anderson said Yorkshire, the country's third biggest building society, had 80 branches in areas where Britannia did not and Britannia had 135 where there were no Yorkshire outlets.
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