The union claims most people would back the change

The protests will be used to put pressure on parties in the run-up to a May general election, the Rail Maritime and Transport union said.

Returning railways to the public sector would save money and have the support of most of the population, it claimed.

The government said the move would be a waste of billions of pounds, "without a single rail being replaced".

The first rally will take place in Glasgow on 16 April, with the final march in London two weeks later.

The core of the rallies will be a group of 30 men and women representing rail workers across the country.

Different companies

RMT general secretary Bob Crow told BBC Radio 4's Today programme that opinion polls showed renationalisation was supported by 65-72% of people.

The reality is that re-nationalisation would cost billions of pounds without a single rail being replaced Department for Transport

"The railways can only be run by a joined up railway," he said. "You can't have individual different companies out there.

"The fact is it would be cheaper for the British Government to renationalise it rather than bung three times the amount of subsidy that the former British Rail received."

The rallies would be "a serious attempt to mobilise public opinion and put pressure on the government," Mr Crow said.

'Not affordable'

The Department for Transport said the government's position was set out in the Future of Transport white paper in July 2004.

"It stated that the railways should remain a public private partnership, as is common across Europe," a spokesman said.

Bringing the railways back under public control was not affordable, he added.

"The reality is that renationalisation would cost billions of pounds without a single rail being replaced."