The House of Commons Public Accounts Committee has submitted evidence to the review of the Garden Bridge project conducted by Dame Margaret Hodge MP.
"The story of the Garden Bridge is a sorry tale about how high profile individuals with the ear of the powerful Mayor of London can gain access to funds with little risk," said Meg Hillier MP, chair of the PAC, as her committee submitted its formal evidence to the review commissioned by the Mayor of London.
Although the PAC has not taken a formal position on the Garden Bridge, MPs on the cross-party committee are said to be concerned about the risk to taxpayers' money.
Ms Hillier said: "At each stage it is taxpayers who have footed the bill.
"The London taxpayer has been doubly hit. In addition to central Government putting in £30 million, TfL has also contributed £30 million for a project that seems largely for the benefit of tourists.
"With an already stretched budget, TfL can ill afford this and there are still important questions about who would pay the ongoing maintenance of the bridge which the Mayor’s review needs to get to the bottom of.
"All this public money has been pledged without a convincing business case. The timetable has now slipped so there is serious likelihood that if the bridge gets the go-ahead it will clash with work to build the Thames Tideway Tunnel.
"Wishful thinking and a close relationship with the Mayor are not the basis on which central Government should be spending taxpayers' money.
"Even when officials made their concerns clear the minister overrode them, potentially throwing good money after bad to protect taxpayers' original investment.
"If the promised private investment fails to materialise this muddled thinking will result in a poor deal for taxpayers.
"The Permanent Secretary of the Treasury has committed to providing our Committee with his own analysis of the business case for the Garden Bridge and we look forward to receiving this soon."
In response to Ms Hillier's remarks, the Garden Bridge Trust drew attention to its statement of 11 October issued in the wake of the National Audit Office report.
At that time, the trust affirmed the status of the bridge as a "visionary project" and argued that once loans and VAT are taken into account, the net public contribution to the Garden Bridge is in the region of £20 million.