Union leaders have warned of job losses and closures under plans to franchise more Crown Post Offices under a “modernisation” programme.

The Post Office announced plans to make changes to 42 crown offices, including three closures, which it said would affect 400 workers.

But the Communication Workers Union said up to another 50 branches face being franchised in the next two years, with a total of 1,000 affected by the proposals.

The Post Office argues that moving crown offices - the larger branches usually on high streets - to other sites such as retail outlets maintains and improves services.

But the union said the move is “condemning the service to decline”, and pledged to campaign against the proposal as well as consulting its members on what action to now take.

The CWU said the announcement confirms the Government is attempting to privatise the Post Office following the sale of Royal Mail.

Roger Gale, the Post Office’s general manager of the crown network, said: “In some locations, directly-run Crown Post Office branches work well but in others there are alternatives, such as franchising, which can work better for the business and its customers, not just in terms of access to Post Office services but also in relation to long-term viability.

“We need to continue to make changes to strengthen the crown network and we have today announced that we are seeking suitable potential retail partners to work with us on providing franchised services for 39 branches and we are proposing to close three branches in areas where it is no longer viable to keep a crown branch.

“Losses in the network of Crown Post Office branches have been successfully reduced from £46 million a year in 2011/12 and, overall, this part of the network is now breaking even.

“But with high property costs and restricted growth opportunities in some locations, some crown branches will not be able to make money.

“We must address this and, like any high street retailer, we have to continue to adapt to customer demands, which our network must reflect. We cannot look to the taxpayer to subsidise crown branches that lose money.”

CWU assistant secretary Andy Furey said: “This is devastating news for our members. It is death by a thousand cuts. The proposals disregard the wealth of expertise, experience and sense of pride in public duty which is shared by Crown Post Office employees.

“Post Office Ltd should never have been separated from Royal Mail. It should be developing services with Royal Mail and Crown Post Offices should be a one-stop shop for mail, banking, financial and retail services.

“This trusted public service is being destroyed by lack of imagination and a dash for cash when what it needs is innovation.

“Downgrading the crown offices is blatant privatisation and the Post Office is getting away with not going to Parliament for discussion on this by MPs. The Post Office is publicly owned, so presumably the Government has approved this.”

CWU deputy general secretary Terry Pullinger said: “Tragically, this is yet another horrendous example of broken promises, irresponsible government and chronic mismanagement by the Post Office.”