Controversial plans to privatise Royal Mail has come under fresh attack after subpostmasters were urged to refuse to stock information on how the public can buy shares.

The National Federation of SubPostmasters (NFSP) attacked a bid by the Post Office to ask its members to promote the sell off.

The federation urged its members to reject the call, pointing out that a privatised Royal Mail could be "catastrophic".

The NFSP has joined other groups in calling for a halt to the privatisation plans, warning that the government has failed to deliver a secure future for the UK's post offices.

A third of all income earned by subpostmasters comes from sales of Royal Mail products and the NFSP predicts "mass" post office closures if that income is jeopardised.

NFSP General Secretary George Thomson said: "I am surprised and angered by POL's request for subpostmasters to act against their own interests by encouraging the public to back the sale by buying shares.

"Subpostmasters are acutely aware that ministers are taking a gamble with the future of our post offices by selling off Royal Mail."

The Communication Workers Union is threatening to hold a strike ballot among its members unless a deal is reached soon on pay, pensions and other issues linked to privatisation.