A British judge blocked a stoppage planned for next week by railway signallers on Thursday, effectively halting Britain's first national rail strike in 16 years.

The strike, over jobs cuts and changes to working conditions, was expected to cause widespread disruption on the national rail network as millions of commuters returned to work after the Easter holidays.

The signallers' strike would have deeply embarrassed Prime Minister Gordon Brown, who is expected to announce the date of a national election next Tuesday, the day the signallers were due to start their four-day strike.

Brown's Labour Party, trailing in opinion polls before the expected May 6 election, receives most of its funding from unions and its opponents have used a bout of industrial unrest to attack the party for its union links.

A strike by railway maintenance workers from April 6 may still go ahead but it is likely to cause far less disruption because management believes it can keep services running.

Justice Victoria Sharp ruled in favour of rail infrastructure operator Network Rail which had sought an order to block the strike, citing irregularities in the strike ballot, the Press Association news agency said.

The signallers had been due to stage two four-hour stoppages a day, during peak hours, for four days from April 6.

Unions say 1,300 planned job cuts and changes to staff rosters would affect safety, a charge denied by Network Rail.

Plans for new ballot 

The RMT union, representing signallers, immediately said it planned to call a new ballot on strike action.

RMT General Secretary Bob Crow said: "This judgment is an attack on the whole trade union movement and twists the anti-union laws even further in favour of the bosses."

"Our executive will meet this evening with a recommendation for a re-ballot," he said.

Network Rail's head of operations, Robin Gisby, said train services would run normally next week. "This is good news for the millions of passengers who rely on us every day, and for our freight users and for the country as a whole," he said.

"We have a responsibility to our people to continue talking to the unions to find a settlement," he said.

Transport Secretary Andrew Adonis urged unions and management to resume talks. "It is now vital that the two sides in this dispute get back round the table as soon as possible to negotiate a settlement."

Network Rail said the RMT union had balloted 11 signal boxes which no longer exist. In other locations, the number of members balloted was larger than the number of employees, it said.

British Airways cabin crew held two strikes last month and the Unite union has threatened to call a third strike after Easter if there is no progress in its dispute with management over changes to working practices.

Reuters