A rebellion by Labour MPs against contentious plans to shrink the post office network saw the government's majority reduced from 67 to 20 last night, in a vote on a Conservative attempt to impose a freeze on closures.

About 20 Labour backbenchers defied the government whip to support the Tory motion calling for a halt to plans to close 2,500 post office branches. The scale of the revolt underlined the political sensitivities of the issue.