Arup’s infrastructure director for London, Alison Norrish described the multiple contracts for building stations as a challenge and said many interfaces between different packages of work created problems.

On site at Liverpool Street, she explained, there were different contracts for building diaphragm walls, entrances, lining the tunnels, fit out and systems installation. “The interfaces involved were absolutely extraordinary and fundamental to the delays that have knocked on,” she said.

Alison added that the size of site for contractors operating at Moorgate is barely bigger than the shaft opening itself. Future construction sites, she went on, should be larger to allow works to be carried out more effectively and efficiently. “Keyhole surgery looks good on paper, but we should construct on reasonable sites.”

But she also said that when Crossrail opens, she believes the memories of the project’s difficulties will fade “and we will be seriously proud that we delivered this”. The “cathedrals in the ground” she continued “will be much beloved by Londoners in the future.”

Delegates to the conference, organised by the Policy Forum for London, also heard from London Borough of Bexley’s leader Teresa O’Neill who called for Crossrail to be extended east to Ebbsfleet.

“What is proposed at the moment is not finishing Crossrail; the original proposal actually joined it up to Ebbsfleet,” she said. “In 2008 (former Chancellor) George Osborne decided to stop it at Abbey Wood, but the business case (for the extension) has never been undermined.”

Teresa reminded delegates that Sir John Armitt’s 2050 vision for the Thames Estuary, published last year, supported an extension of Crossrail to Ebbsfleet to deliver jobs and homes.

“Bexley doesn’t have a Tube, we have a heavy reliance on railway, buses and the car. You can stand in Thamesmead and see City Airport, but not many residents work there as it is too hard to get to.” Extending the line to Ebbsfleet will, she added, bring improved connectivity to central London, the City, Canary Wharf and Heathrow airport and provide extra transport capacity.

“The irony is the overspend on Crossrail 1 would have more than paid for (the extension),” she said. Whatever the result of the General Election on Thursday, added Teresa, she will be “banging on Government’s door to get this going again”.

(Photograph: Crossrail)