Rail unions described "madhouse" economics yesterday as foreign state-owned companies began bidding for Britain's publicly owned East Coast Main Line.

The Channel Tunnel's operator Eurostar confirmed yesterday it would enter the fray in a joint bid with French company Keolis to take over the route, which runs from London to Scotland.

Transport Secretary Patrick McLoughlin first announced the sell-off in March, describing the system of franchising - leasing operating rights to private bidders rather than public ownership - as a "force for good in the story of Britain's railways."

But galled union leaders said the Eurostar-Keolis bid would effectively see passengers in Britain subsidising European railways.

Eurostar's majority shareholder is France's national state-owned railway company SNCF, while its minority shareholders are the National Railway Company of Belgium and London and Continental Railways - a private company that had to be nationalised in 2009 after running up £5.1 billion worth of debts.

Keolis is ostensibly a private-sector firm - but it too has SNCF as a majority shareholder.

Transport Salaried Staff Association general secretary Manuel Cortes said the coalition's privatisation agenda had ended in "the economics of the madhouse."

The government had already shown it was happy to let German, Dutch and French state-owned companies run franchises in Britain at a profit, he said.

"But for reasons of political dogma, it refuses to let English publicly owned companies like East Coast continue its own successful franchise," he said.

Train drivers' union Aslef's leader Mick Whelan decried the privatisation push as "shameful," while Rail Maritime and Transport union general secretary Bob Crow said ideology alone had spurred the sell-off.

The route had even won plaudits from the Office of Rail Regulation in May after the watchdog found it required the lowest level of government funding relative to income of any rail operator, requiring a top-up of just 1.2 per cent.

"The truth is that any state rail operator can run trains in the UK other than the British state, despite the obvious financial benefits.

"That is Thatcherite ideology from the outer limits," he said.

The Department for Transport is expected to select the winning bidder next October.