Sadiq Khan, the new mayor of London, has given his backing to the Garden Bridge project.

Above: Some 270 trees and more than 100,000 plants are to be planted on the bridge

Mr Khan was previously considered to be sceptical about the project, having shared widely-held concerns about the probity of the design procurement process and the structure’s absence from any previous infrastructure needs assessment study.

However, he has now given the project his support – with a few conditions. He wants it to be closed less often for private events, and he wants children to be involved in the gardening.

The mayor said that the bridge “must be a genuinely public and open space for all Londoners, rather than a closed and private space”.

He said: “I expect the Garden Bridge Trust to ensure that the bridge be closed fewer days each year for private fundraising events and fewer hours when they do. I also want a guarantee that an ongoing programme of visits will be laid on for local school children.

“The Trust must also look to build a strong working relationship with parks from all over our city, so that seeds and plants grown on the Garden Bridge can then be replanted in parks across the capital – ensuring it has a positive benefit for all Londoners.

“The early days of this project clearly fell short of our expectations on transparency. I am determined to run the most open and transparent administration London has ever seen. I will let the sunshine in, which is why we are today publishing the previously undisclosed full business plan for the Garden Bridge alongside a list of its funders.”

A Garden Bridge Trust spokesman said: “We welcome the mayor’s support and look forward to working with him and his team to make the beautiful Garden Bridge happen and deliver its many benefits to millions of Londoners and visitors to the city.

“We share the mayor’s desire to have the bridge open to everyone for as long as possible. Balancing this and the need to raise the required private funds to operate the bridge is important.

“We also share the mayor’s desire to involve young people. We already have a youth board made up of over 40 local students, who will be taking an active role in developing our education and schools programme. We are also progressing partnerships with local green initiatives and charities and look forward to developing these further and building on the mayor and the trust’s shared aspirations.”

The Garden Bridge Trust expects to be able to deliver the bridge for a cost of £175m. So far it has raised £145m in public grants and private donations.

A Franco-Italian joint venture of Bouygues Travaux Publics and Cimolai SpA has been awarded the construction contract and is expecting to start work this summer, completing in late 2018.