British designer Thomas Heatherwick has launched an impassioned defence of his Garden Bridge project in London, arguing that the project has been used as a political football by “people with an agenda” and those “who love to sneer.”

The scheme – a 367m (1,200ft) planted River Thames crossing linking South Bank and Temple – has attracted controversy and negative headlines over the allegedly opaque procurement process and the public funding required to build it.

Heatherwick hit back at his critics on the BBC’s Newsnight programme, stating that any rejection of the project at this stage would show that “we have suddenly become a society who have no confidence in ourselves”.

"There's all sorts of people who want to get their little agenda and pin it onto this project,” he said. “But it’s an amazing project. How can it possibly be a bad thing to stitch the city together better, to create new public space that we have never had before, to create new views for all of us?”

The designer said decision-makers must “hold their nerve” over the project.

However, a Newsnight report uncovered a £22m funding gap that will raise more questions about who will shoulder the cost of the bridge. According to the BBC, several private funders withdrew over the last year, and what had been previously estimated as a £30m shortfall is actually closer to £52m.

The Garden Bridge Trust must raise £175m to complete the project. The government has already agreed to provide £60m of taxpayers' money, but the additional £115m must come from the private sector, companies and individuals.

A spokesperson for the Trust told Newsnight: “Last year a small number of pledges made by interested organisations did not progress to formal funding contracts."

Lord Davies, chair of the Trust, conceded less money had been raised than claimed and said delays to the bridge had seen costs rise by £10m. However, he too defended the project and said “it sums up what's great about Britain".

Heatherwick vowed to continue pushing for the bridge by “working with whoever is in power to try to do the best public project for all of us.”

“The government has supported the project because they can see transportation benefits, the national dimension and a [link with] society that stitches right back to our history," he added.

"This project will be finished three years from now and we'll be walking across there with our children and with our grandmothers. They’ll have the best view of the city, which is from the centre of the river where the buildings get out of the way."

A joint venture of contractors Bouygues Travaux Publics and Cimolai SpA was hired in March to begin preliminary work on the project. However new London mayor Sadiq Khan called a temporary halt to proceedings last month while further scrutiny of the public finding required was carried out