The major Hammersmith Bridge refurbishment project will be delayed into the New Year, with the estimated cost of the work rising by £11 million.

The historic bridge was set to be closed for repairs by late 2018, but local leaders say the complexity of finalising the major engineering plans has set it back.

The work will close the bridge, used by 20,000 vehicles a day and subject to weight restrictions for decades, for an unconfirmed period.

The delay is causing costs to mount for Transport for London (TfL), which wants the bridge owned by Hammersmith & Fulham Council (H&F) strengthened to allow double decker buses to drive over it.

Figures provided to London Assembly transport committee chairman Caroline Pidgeon say TfL had spent £546,000 by August on traffic wardens stationed at either side of the bridge to monitor weight restrictions.

City Hall officials also wrote that TfL said H&F had told the transport body work was likely to start in the autumn of 2019.

However, H&F says it did not know where that date came from, saying detailed planning was still under way, and the project is yet to be put out to tender.

"We don’t know why the Mayor’s office has given a start date of autumn 2019. This is neither a date we recognise, nor one we’ve discussed with TfL," a spokesman said.

"There is no confirmed start date yet, but we will work with TfL to ensure residents are kept well informed with any updates."

TfL added: "Hammersmith Bridge is owned and maintained by Hammersmith & Fulham Council and we continue to work with the council on their plans to repair it.

"We are talking to the council about timescales and the cost of the repairs so that these can be finalised over the coming months."

Hammersmith Bridge in London is due to have extensive repair work
Hammersmith Bridge is due to undergo extensive repair work

Papers being presented to the council's leadership on November 5 show the provisional price-tag has risen to £36m from 2014's £25m estimate.

TfL and the London Bridges Engineering Group were to shoulder the bulk of this, loaning £1.5m over two years to H&F for the shortfall.

Ms Pidgeon said she had been asking for clarity on a timeline for the work.

"This is a really strange situation that has been going on for some time and Hammersmith & Fulham is not being open about what's really going on," she said.

She added that if the problem was financing or complex works, H&F and TfL should provide more detail to the public.

H&F's spokesman rejected the suggestion of financial reasons for the delay, saying it was updating the public and other boroughs regularly via its website and in letters.

But Ms Pidgeon warned that TfL, already facing road maintenance budget cuts and the cost of Crossrail delays, needed to get the refurbishment under way before financial pressures worsened.

"TfL are having to pay with public money on these bridge for wardens when it should be paying for works to fix this situation," she said.

The Grade II listed bridge has survived the Blitz and a bombing but has been frequently closed for repairs, as its Victorian era engineering was not designed to bear modern traffic loads.

Interim repair works have been meticulous, tools must be custom-built and whenever one of the bridge's 999 decking panels needs replacing it takes six hours to do so.

Richmond Council transport lead Alexander Ehmann said the Liberal Democrat administration did not support the previous Conservative leaders' call for Richmond to take over the project.

However, Cllr Ehmann said Richmond wanted to plan its traffic management, and riverside residents and bridge users needed clarity too.

He added: "The bridge needs investment, and it needs strengthening works, and it needs a repair timeline. I would like to see that sooner rather than later."