Garden Bridge has already cost public purse nearly £10 million

The revelation comes in the newly-signed funding agreement between Transport for London and the Garden Bridge Trust for the £60 million of public funding for the £175 million river crossing.

Transport for London has pledged £30 million whilst the same sum will be provided by the Department for Transport.

However, TfL will hold back £9.7 million in recognition of the money it has spent on the project to date.

“I personally find it staggering that so much public money has already been spent on the Garden Bridge when so many questions still need to be answered, especially over the procurement of its design contract," said Caroline Pidgeon AM, leader of the Lib Dem group on the London Assembly.

Sir Peter Hendy – the outgoing TfL commissioner – recently promised a review of that procurement process.

The funding agreement requires the trust to "actively raise funds on a continuing basis to meet the ongoing operation and maintenance of the Garden Bridge".

The Garden Bridge Trust still needs to raise £48 million towards the capital cost of the bridge.

• Read the funding agreement in full