Postal workers threw down the gauntlet to Labour today, urging the party to scupper the Con-Dems' plan to sell Royal Mail by pledging to immediately renationalise the much-loved service if elected in 2015.

Writing exclusively in today's Morning Star, Communication Workers Union (CWU) leader Billy Hayes called on Labour to back the campaign against privatising the world's oldest postal service.

Mr Hayes is seeking support for the union's plan of action, including a national postal workers' strike, at Labour's annual conference in Brighton.

Conference will debate Royal Mail this week and the CWU wants Labour to take back Royal Mail "in the event of the coalition government actually selling the company."

It follows a unanimous vote by unions for the CWU's anti-privatisation motion at TUC Congress earlier this month.

"If the party conference comes out strongly and explicitly for renationalisation in the event of a sale then this cannot fail to have an impact on potential investors," Mr Hayes writes.

"They will surely understand that from party conference there will be a strong campaign for a Labour government in 2015 to quickly overturn the sale."

Pressure is also building on Ed Miliband from Labour MPs opposed to privatisation.

North Ayrshire and Arran MP Katy Clark, also writing in today's Star, called on Labour leaders to promise to bring Royal Mail back into public ownership.

"A privatised Royal Mail will be under huge pressure to cut staff conditions, increase prices and reduce the services it provides to compete with such companies.

"Labour has vigorously opposed privatisation.

"Everything we do and say now will be under scrutiny as private investors take a view on whether to purchase shares once they are finally floated on the stock exchange.

"I still believe it is possible to stop this privatisation.

"Let's do everything we can at this conference to make sure that Royal Mail stays in public hands."

The deeply unpopular sell-off, strongly contested by Labour and Tory constituents alike and which even Thatcher thought "a step too far," has provoked the Scottish National Party to announce that it will renationalise Royal Mail in Scotland if it wins next year's independence vote.

Scottish First Minister Alex Salmond called on Mr Miliband to match the SNP's pledge.

He argued that "common ground between the Scottish government, your delegates, the trade unions and the vast majority of the public in opposing this sale across the UK" provided an "opportunity to stop this misguided sale in its tracks."