As MPs backed plans to close at least 3000 post offices in towns and cities, the Conservatives have blamed ministers for undermining the viability of the network.

Approval for the compensation package for sub-postmasters who resign means that the Post Office will be able to identify which branches are unviable and should shut.

Stephen Timms, the industry minister, said the alternative was an unplanned spiral of decline.

The government has already announced that £210 million will be made available to compensate subpostmasters and improve the remaining Post Offices.

The shadow trade and industry secretary, Tim Yeo, accepted that "some urban post offices must be streamlined and modernised".

"But the government's mismanagement and delay over the future of the network is risking the livelihoods of thousands of employees, and the quality of service provided to millions of customers," he said.

"Unfortunately their future was undermined by Labour's removal of 40 per cent of their income in a decision that will end the availability of cash benefits through Post Offices which recipients find invaluable.

"Labour's promised solution, however, will not make these businesses viable and it will not allow benefit recipients to receive payments in cash. It will, however, spend £210 million of public money in an attempt to cover up the consequences of government mistakes."