Charity behind London project admits it has no idea how much the final bill will be

The Garden Bridge Trust has said it will be asking the public to help plug a £50m-plus funding gap so it can build the bridge.

The bridge has already risen £10m in cost to £185m but in the charity’s latest report and accounts the Trust says the costs could go up again – and admits it has no idea what the final bill could be.

The Trust said: “Due to the hurdles still to be cleared and the ensuing delays the final cost could substantially exceed the formal estimate. Until the hurdles have been overcome and the subsequent programme refined we will not obtain a definite estimate. Nevertheless we have developed an update fundraising strategy that reflects the increased costs.”

A public fundraising campaign, the Trust said, “will offer a range of ways in which the public can get involved and support the project. This is expected to generate funds but also raise public awareness and support.”

It is also looking at setting up an Endowment Fund to help with the estimated £3m annual running costs.

Contracting joint venture Bouygues and Cimolai had been expecting to start construction this summer.

The news comes as the chairman of the Garden Bridge Trust admitted that the charity cannot be considered a going concern because there are too many risks associated with the scheme.

In report and accounts filed at Companies House, Lord Mervyn Davies said that trustees “are unable to conclude that the Trust is a going concern and feel it only appropriate to flag these risks in this report”.

Davies said the main risks facing the scheme – and the Trust – were securing land on the South Bank, getting confirmation from London mayor Sadiq Khan to guarantee the £3m running costs promised by previous mayor Boris Johnson, plugging the current £56m funding gap and making sure it has enough promised cash ahead of planning consents running out at the end of year.

In his report, Davies admitted: “It is hoped that these will be resolved over the months ahead but since a number of these matters are outside the control of the Trustees, they recognise that if this is not possible, they will need to considered the further delay to the project, and in a worst case scenario, whether the project remains viable.”

Construction work on the Thomas Heatherwick-designed bridge is already months behind schedule with the Trust being forced to rip up a previously stated timetable of starting on site last summer.

Under this plan, preparatory works were supposed to have started last spring with the scheme due to have been completed by summer next year.

The report added: “Provision of the mayoral guarantee is also a requirement of our planning permission [local authorities have said they will not pay for the upkeep of the bridge] which will expire in December 2017. For construction to commence prior to this, remobilisation of the construction team will be required during early summer 2017.”

Davies also blamed a number of factors for the already announced hike in cost including the EU referendum, a change in mayor and the installation of a new prime minister. The Trust says it has £129m of funding in place – £60m of which is taxpayers’ cash.

In the accounts, the Trust said it had spent £28.6m in the year to March 2016, up from £5m the year before. The bulk of this, just over £26m, was spent on pre-construction costs, while a further £1.6m was shelled out on fundraising activities. Operational costs came in at just over £423,000. Its income during the period was £39.2 million. The Trust said it was carrying forward funds of £15.6 million.

The number of salaried staff at the Trust was eight who shared £477,000 in wages with three people earning £60,000 or more. The salary of the highest paid staffer, who is not named, was between £110,000 and £120,000. It also paid out £465,000 in temporary and contracted staff.

The price for the project was originally estimated at £60m when it was launched three years ago. Back then it was expected to be completed this spring.