Wisbech's main post office is one of 70 earmarked for closure if its facilities can be relocated to a nearby shop or supermarket, it emerged last night.

Union leaders accused the Post Office of delivering a 'huge blow' to its network after it announced plans to seek 'partnerships' with retail firms for almost a third of its main high-street branches.

The company said the move would help the offices remain in their current locations, pledging no compulsory redundancies.

But the Communication Workers Union (CWU) described the decision as the 'partial destruction' of the so-called Crown office network.

It said staff were in 'shock' at the move, which would have a big impact on the high streets of small towns.

The Post Office said its 375 Crown offices were losing £40m a year and it was seeking to link up with national partners, or local firms. It added if it could not find a suitable deal, the Crown office would remain.

'We are currently undertaking the biggest business transformation programme in the history of the Post Office,' it said. 'Our investment will maintain the size of the network and modernise branches to meet customer needs.

'Crown branches are a fundamental part of our long-term growth strategy and need to be brought into profit, currently operating at a £40m annual loss.

'The Post Office successfully works with many partners and in some areas it is more viable to partner with quality retailers. There are no compulsory redundancies planned as part of this strategy.'

Five years ago, King's Lynn's main office was moved from Baxter's Plain to the nearby WH Smith, in Norfolk Street. There is a WH Smith close to Wisbech Post Office, but is not yet clear whether it will offer it a new home.

Billy Hayes, general secretary of the CWU, said: 'Staff will be in shock at the scale of what will effectively be the closures of Crown post offices across the country.

'This move will have a huge impact on the high streets of small towns earmarked to lose their Crown post office.

'These offices provide a dedicated specialist service to communities which will not be replicated by a window or two in a bigger shop.'

Town, district and county councillor Samantha Hoy said: 'I'd rather have it safe somewhere else than closed.

'My only concern is there are always large queues in that post office and will WH Smith be able to handle it?'