The Mayor Of London is understood to have serious concerns about the government's multi-billion plans to build a high-speed railway line between London and Birmingham, according to a leaked document seen by the Sunday Telegraph.

Boris Johnson has branded the proposed line 'perverse' and 'inadequate' in a letter to a group which opposes the £34bn line. His comments will cheer many Conservative MPs representing seats in London's green belt, who privately question the merits of the scheme.

The new line would cut through acres of countryside in Tory-held seats north of London.

When it entered office the government decided to overturn Labour's plans to build a third runway at Heathrow. Ministers believe the high-speed rail line would ease congestion on the existing West Coast Mainline and provide an alternative to air travel within the UK.

Although Conservative MPs rarely voice concerns about the viability and cost-effectiveness of the line, many believe the project could be an expensive white-elephant which would only be affordable for business-class commuters.

Members of the Commons Transport Committee have recently questioned whether it would be cheaper to expand the existing West Coast line, rather than building a new one through some of England's most picturesque countryside.

As the Tory website Conservative Home points out, this isn't the first time Boris Johnson has questioned the merits of the new line. The Mayor of London is increasingly criticising coalition government policies, particularly on changes to housing benefit. Political commentators expect Boris to increasingly distance himself from some of David Cameron's policies in the months leading up to the elections for the Mayor of London next May.