Over 80 London business leaders have written to the government offering to help pay for Crossrail.

In a joint letter to Alistair Darling, the transport secretary, they said they were willing to accept a one-off levy on business rates in order to secure the Heathrow to Canary Wharf link.

The leaked letter, written in March, said: "You have called for a 'very substantial contribution' from the business community. We are willing, in principle, to support a supplementary levy on business rates hypothecated to Crossrail, if that is necessary to secure the delivery of this unique scheme."