Customers should abandon banks that refuse to let them use the Post Office to carry out transactions, the employment minister has said.

In a speech to the LibDem conference in Birmingham on Monday, Ed Davey has announced that Nat West intends to join Barclays, Lloyds and the Co-op in allowing its customers to bank at post offices.

He is also chastised HSBC and Santander for refusing to follow suit.

"Frankly, that’s really disappointing," he said. "So today, I hope you will join me in calling on them to think again."

"And if they don’t respond, maybe we need another campaign. To tell these banks they have a responsibility to their customers and local communities. And if they still don’t listen. Well, I hope you will think about switching your account to another bank."

The move is designed to help stem the tide of post office closures. A recent study by Consumer Focus suggested that more than 18 million consumers would be likely to use post offices, in addition to their bank branches, to access their current accounts.

With 11,800 branches, there are more post offices in the UK than there are bank branches.

Ministers also want the Post Office to become the “front office” for government, taking charge of administering services, such as council tax payments and parking permits.

Davey claimed that four thousand post offices will be "transformed" over the next few years as a result of investment spearheaded by the LibDem chief secretary to the Treasury, Danny Alexander.

And he attacked Labour for viewing the Post Office as "not cool enough" to bother saving.

"The reality was that New Labour just didn’t get it. Post offices just weren’t cool enough for Tony Blair and his Cool Britannia mates. The fact that old people, poor people, real people depended on them didn’t matter to the likes of Peter Mandelson," he will say.

"That is why we had the obscene spectacle of a Labour government – a Labour Government - paying the owners of sub-post offices to pack up and go home."