Around 2,000 railway workers across the West Midlands are being balloted on a "derisory" four-year pay offer which threatens the UK's first national rail strike for more than 20 years.

A two-week ballot of Network Rail infrastructure staff and signalmen will decide if workers vote for industrial action which could bring the UK's entire rail network to a halt.

And RMT Midlands regional organiser Ken Usher warned the union was pressing for a 'yes' vote to industrial action in protest at Network Rail's four-year pay offer.

If the ballot, which runs until May 12, results in a vote for strike action, Mr Usher said passengers would be caught up in the first national rail strike since 1994.

RMT members in the West Midlands were meeting in Birmingham last night for an update on the dispute.

"We have been in pay talks for quite some time and Network Rail has come up with a derisory offer of a £500 non-consolidated lump sum for 2015, and RPI inflation for 2016, 2017 and 2018," he said.

"We want to encourage members to vote 'yes' for strike action and for industrial action short of a strike.

"If we get a 'yes' vote to both questions, there is the serious likelihood that we will have the first national stoppage for more than 20 years.

"There would be total chaos the length and breadth of the UK, with the entire network affected."

In a message to 17,000 members being balloted nationwide, the RMT said: "Network Rail has tabled a final four-year pay offer to the unions.

"The deal involved a pay freeze in year one - that amounts to a real terms pay cut.

"On top of that, job protection guarantees will expire this year with no assurances into 2016 and the travel concession arrangements are also seriously undermined."

Network Rail said talks had concluded earlier this month with a "new, revised offer".

Phil Hufton, managing director of Network Operations, said: "We have had very constructive talks with our trades unions and we appreciate their contribution to those discussions.

"We believe the revised offer is the best one we could achieve through negotiations which have now concluded.

"The trades unions negotiating team now need to take the offer away to share with their leaders and local / area representatives with a view to reaching an agreement.

"We believe such an agreement would be good news for our people, for Network Rail, for our trades unions and, most importantly, for the people we are here to serve - our customers and passengers."