Transport for London has denied that Silvertown Tunnel construction costs have risen by £200 million - claiming the apparent increase was due to the wording of the contract.

The document, which has only just been made public despite being signed in November, indicates that the 'total value of the procurement' was £1.2 billion - up from the £1bn previously set out.

But a TfL spokesman explained: 'The costs have not gone up - it's just the way the total value of the design, build, finance and maintain contract is expressed.

'The construction is still £1bn as we have always said.'

The design, build, finance and maintain contract to construct the new road link between Silvertown and North Greenwich was awarded to the Riverlinx consortium - a five-strong group led by Aberdeen Standard Investments - last year.

The TfL spokesman added: 'There have been no increases in the overall price of the project, and the basic construction value is around £1bn as we have always said.

'The figure referenced in the contract includes expenditure already outlaid by TfL, plus the cost of debt up to the forecast opening date in 2025.'

Once the Silvertown Tunnel opens, both it and the Blackwall Tunnel are due to introduce user charges.

The cost for each type of vehicle are yet to be determined but the money will be used to pay for the construction and maintenance of the new tunnel, with TfL saying it is a legal requirement as part of the planning approval.

London Assembly Member Caroline Pidgeon called on the project to be cancelled, with the money used to improve the Tube network instead.

The Lib Dem politician said: 'Silvertown Tunnel is already turning out to be a hugely expensive construction project and I expect its financial cost will escalate even further.

'There are real alternatives to building an expensive motorway under the Thames.'

A spokeswoman for the Mayor of London said: 'It is essential that we continue with plans for more river crossings in east London.

'A new tunnel at Silvertown is important as the existing infrastructure is both antiquated and worn out.'