Taxpayers face £22 million bill if Boris Johnson's Garden Bridge project collapses, watchdog warns

National Audit Office finds a “significant risk” the crossing will not be built - and highlights Cameron's personal intervention to fund it

David Cameron, pictured on the day he resigned as prime minister, personally intervened to approve extra taxpayer funding for the Garden Bridge project (Getty)

Taxpayers face a £22.5 million bill if London's controversial Garden Bridge project collapses, a highly-critical watchdog’s report has warned.

There is a “significant risk” the Thames river crossing – championed by Boris Johnson – will never be built because it faces a funding shortfall of up to £75m, the National Audit Office (NAO) found.

Furthermore, the proposed pedestrian bridge and garden has already been delayed by 18 months, because of problems obtaining some of the land it needs.

And, if it is scrapped, the NAO concluded, the Department for Transport (DfT) stands to lose a maximum of £22.5 million of the £30 million it has allocated to the project.

The watchdog’s scathing findings included that:

* The initial £30 million was committed by then-Chancellor George Osborne to Mr Johnson, then-London Mayor, without any involvement of the DfT.

* That investment was made despite an assessment of the business case finding there was a “significant risk” that the bridge could represent “poor value for money”.

* Government ministers ignored the advice of civil servants not to extend funding to the Garden Bridge Trust on at least two occasions.

* On the second occasion, then-Transport Secretary Patrick McLoughlin over-ruled civil servants to extend taxpayers' exposure and underwrite liabilities of £15 million if the project did not go ahead.

* That ministerial direction was issued after Cabinet Secretary Sir Jeremy Heywood wrote to the DfT to make clear the “frustration” of David Cameron and Mr Osborne at perceived hold-ups to the funding.

* The DfT sought to protect taxpayers' money by capping the amount which could be spent by the trust before construction began at £8.2 million – but later relaxed that cap on three separate occasions.

“Officials from the department advised ministers against increasing the department's exposure for the second and third increases,” the NAO said.

Meg Hillier the chairman of the Public Accounts Committee (PAC), which oversees the NAO’s work, said: “It worries me that whenever the Garden Bridge Trust runs into financial trouble, the Department for Transport releases more taxpayers' money before construction has even started.

“If the project collapses, taxpayers stand to lose £22.5 million. If it goes ahead, who is going to pick up the bill to maintain it?”

But the Garden Bridge Trust said it had raised nearly £70 million of private money and was working on finalising the land deals required to build the south landing.

It pointed out that 78 per cent of the project cost would be raised from private finance.

For the Government, transport minister Lord Ahmad insisted it “remains supportive of the Garden Bridge project”.

He added: “Ministers took into account a wide range of factors before deciding whether or not to make funding available.

“The taxpayer, however, must not be exposed to any further risks and it is now for the trust to find private-sector backers to invest in the delivery of this project. We will consider the NAO's findings carefully.”