Computer simulation of a new high speed train released by the Department for Transport
There has been anger over the government's decision to award a £7.5bn contract to build a fleet of inter-city trains to Japanese firm Hitachi.
The government said the contract for the "super express" trains would "create and safeguard" 12,500 UK jobs.
But the Conservatives said the transport secretary had not provided details to back up the jobs claim.
Unions have called for urgent talks with the government over how much of the work will be done in the UK.
The stock will replace ageing high-speed trains on the Great Western and East Coast main lines.
The consortium awarded the contract, called Agility Trains, is made up of John Laing, Hitachi and Barclays Bank.
The rival consortium which missed out included Bombardier, the only company making trains in the UK, which employs more than 2,000 workers at its Derby factory.
BBC transport correspondent Tom Symonds said the train would be assembled at a factory in Britain, in a location to be confirmed, and its engines made somewhere in Europe. The wheels will be made in Britain but its body shell will be made in Japan.
Transport Secretary Geoff Hoon described the plans as the single biggest investment in inter-city trains for a generation.
He said: "This announcement demonstrates that this government is prepared to invest, even in difficult economic times, by improving our national infrastructure.
"It is good news for the British economy that over 12,500 jobs will be created and safeguarded, good news for the regions that the government is supporting significant inward investment, and good news for passengers that we are taking the steps necessary to improve their rail journeys."
But Shadow Transport Secretary Theresa Villiers said the announcement was "typical spin" from the government.
We need to clarify what on earth is going on and how much work will be done in this country
Keith Hazlewood GMB Union
"Only around 500, at most of the 12,500 jobs, announced today will be created in the UK by the train builder Hitachi and Labour have produced no convincing evidence to back up the rest of their claims on jobs.
"This announcement raises further questions about Gordon Brown's claims about British jobs for British workers. Geoff Hoon needs to stop the spin and tell the UK's hard pressed train manufacturing industry the real truth about his decision on replacing intercity trains."
Agility Trains said it was committed to spending 70% of the contract value in the UK, adding that Hitachi and John Laing expected to create 2,500 skilled engineering jobs in the UK, in train manufacturing, construction and maintenance.
The company added it was in talks with 20 UK suppliers, which would help safeguard jobs in the UK.
But Derby North Labour MP Bob Laxton said the decision was bad news for the area.
"This is a crass decision which gives the Japanese an opportunity of getting into the UK market. I don't believe for one moment the figure of 12,500 jobs because work will be brought into the UK from overseas," he said.
Unions have called for urgent talks with the government.
Keith Hazlewood of the GMB said: "We need to clarify what on earth is going on and how much work will be done in this country."
Bob Crow, general secretary of the Rail Maritime and Transport union, said: "The Transport Department has not answered the basic question of whether these trains will be manufactured in Britain or simply assembled here."
Mr Hoon also announced the Department for Transport was in advanced talks to provide 120 new carriages for the Stansted Express service from London Liverpool Street to Stansted Airport, the order for which is expected to go to Bombardier.
The first of the new trains - which are designed to be faster, greener and able to carry 21% more passengers - are scheduled to enter service on the East Coast mainline in 2013, and to be fully operational from 2015.
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