London's multi-billion pound Crossrail transport link has been given the go ahead by government.

The £10 billion rail project linking East and West London was approved by the transport secretary Alistair Darling on Monday.

In a written statement to MPs he said he was fully supportive of the initiative.

But he cautioned that it was "very, very unlikely" to be ready in time for the 2012 Olympic Games.

"There is a clear transport case for Crossrail and we remain committed to the scheme," Darling said.

"In order to give the project the best chance of success I am assembling an expert team to assess the proposals to ensure they offer good value to London and are deliverable.

"We need to be sure that we have a robust plan for delivering and funding the project, with effective mechanisms to ensure those who benefit from it contribute as fully as possible to meeting the costs.

On Sunday the transport secretary challenged the private sector to get its "cheque book out" to fund the project.

Darling said the proposed congestion-relieving link was "essential" to the capital's future expansion.

But he insisted that the private sector would have to meet a significant proportion of the cost, which he estimated could run to as much as £15 billion.

He told BBC One's Breakfast with Frost on Sunday that the radical rail initiative would not come cheap.

"Crossrail is very important...We believe that it is essential for London's future expansion," he said.

"The big question is how is it going to be paid for.

"Which is why the next stage will be to consult on the route and then go to the people in London who yes we want to pay, and say this is the time to get your cheque book out, because it will have to get a substantial contribution from the private sector because you are talking about a project that could be between £10-15 billion in cost."

However the investment would be worth the effort, the minister claimed.

"It is a huge project, one of the biggest the country would see," he said. "But for the long-term interests of London it is very important."

Darling denied that Crossrail could ever have been ready for 2012.

"It was never going to be in place for the Olympics, we made that clear right from the time we decided to put in a bid for the Olympics," he contended.