The Conservatives tabled a motion in the House of Commons to suspend a programme of 2,500 nationwide closures to allow time for more public consultation.

It was narrowly defeated by just 20 votes after 19 Labour MPs revolted against their own Government, but Mrs Keeble was not among them.

The Northampton North MP instead refused to cast a vote at all, arguing her decision sent a strong enough message to Gordon Brown without embarrassing her party.

"As a Labour member I am expected to vote with the Government, but I am unhappy about the way the closures have been handled in Northampton so I didn't vote," she said. "I was asked several times to vote but I told them I wasn't going to support the Government."

Mrs Keeble said she was surprised the Tory motion was not carried because of the strength of national opposition to post office closures.

The programme of cutbacks, aimed at reducing the Post Office's weekly losses of about £3.5m, has already affected Northamptonshire, and 26 county branches have been ordered to close by May 1.

Mrs Keeble added she did not want to vote with the Conservatives because their proposals were political "mischief-making".

"By not voting with the Government, I left it one vote down, but I wasn't prepared to leave it two votes down by voting against," she said.

"I think most people understand we need to have a viable Post Office network, and if it isn't working, changes are needed.

"What I object to is the way management has handled the whole thing and made a complete pig's ear of the public consultation.

"But even if the Conservative motion had been carried, it wouldn't have stopped the closure programme because it is being run by Royal Mail, not the Government. It was really little more than just mischief-making."

Brian Binley, the Conservative MP for Northampton South, was excused from taking part in the vote because of illness.

But he said it had come too late to save post offices in Northamptonshire anyway.

He said: "I would, of course, have voted with my own party had I been able. But sadly, the battle in Northamptonshire has already been lost."

ed.omara@northantsnews.co.uk