SCOTLAND's core rail link to the rest of Britain faces swingeing cuts, unions warned last night.

The lifeline West Coast Main Line will see "massive cuts to jobs and services" under a new franchise deal expected to be announced tomorrow, the RMT claimed.

Virgin is widely tipped to lose its right to run passenger trains on the railway after rivals FirstGroup reportedly made what industry insiders called a "suicide offer" for the franchise.

But RMT leader Bob Crow yesterday said: "Whoever wins the West Coast route, and all the signs point to FirstGroup, they should be left in no doubt that we will mount a massive industrial, political and public campaign to stop any attacks on our members' jobs and the services that they provide to the travelling public.

"From leaked figures it is clear this franchise is being let with a gold-plated contract linked to massive cuts to jobs and passenger services and huge increases in fares as the winning bidder battles to extract every penny they can in profit."

Mr Crow is a long-term critic of what he calls "casino franchising" but his concerns were last night shared by senior industry sources – and the Opposition in Westminster.

Maria Eagle, Labour's Shadow Transport Secretary, said: "Passengers are set to lose out no matter which companies win these new longer franchises because ministers have promised successful bidders they can hike fares, cut services and close ticket offices."

Services on the West Coast Main Line, which links Glasgow to London and Edinburgh to Birmingham among other key cross-border services, has boomed in recent years.

Passenger numbers have doubled in the past seven years to 32 million a year as falling journey times make the train quicker than the plane for many travellers.

However, Virgin executives are understood to believe officials at the UK Department for Transport are taking further advances in passenger numbers "for granted" and don't understand the role played by their company's brand and image in building them up.

FirstGroup is thought to have offered £6.5bn-£7bn for the 14-year franchise period, which begins in December. That is understood to be £1bn more than Virgin Trains, leaving arguably less to spend on the service. Sir Richard Branson is so angry he has threatened to sue if the First option wins support. In a leaked letter, the entrepreneur – whose Virgin Group owns 51% of Virgin Trains – claimed the only way FirstGroup could meet its commitments would be to "drastically cut the quality of services".

The new franchise lasts until 2026 but some sources contacted by The Herald acknowledged the winner could – to use an expression of Mr Crow – "throw back the keys" if it failed to make a profit of the route. GNER and National Express did that with the East Coast Main Line.

Virgin Trains, part-owned by Perth's Stagecoach, has no other franchises. It will cease to exist if it loses to FirstGroup, the Aberdeen-based transport giant that operates the ScotRail franchise, among others.

A spokesman for the Scottish Council for Development and Industry last night stressed the sheer importance of the West Coast Main Line services to the Scottish economy. He said: "This is a crucial route for Scottish connectivity and for commerce between London, the Midlands and Scotland."

Industry insiders also stressed the railway was as important for Edinburgh and eastern Scotland as for Glasgow. "Too many people forget the capital is to the west of Carlisle, not east," said one.

The Department for Transport is expected to make a franchise announcement tomorrow morning – or later this week – and cannot comment until then.