Transport for London and Crossrail announced the decision at noon today with contractors told to bring sites on the £18bn project to a safe stop as soon as possible.

It is the first major infrastructure project to be locked down following Boris Johnson’s instruction to the nation last night to stay at home.

His announcement triggered confusion across the industry as to whether sites should be kept open or closed.

London Mayor Sadiq Khan said that he believed  “the only construction workers that should be working are those that we need for safety”. But this morning the housing minister Robert Jenrick confirmed on twitter that construction sites could be kept open if it was safe.

Mike Brown, London’s Transport Commissioner, said: “The Government and the Mayor have given clear instructions to stay safe and to stop travelling in all cases other than critical workers making absolutely essential journeys.

“In line with this, TfL and Crossrail will be bringing all project sites to a temporary Safe Stop unless they need to continue for operational safety reasons.

“This means that work on all such projects will be temporarily suspended as soon as it is safe to do so. Essential maintenance of the transport network will of course continue.

“This is being done to ensure the safety of our construction and project teams and also to further reduce the number of people travelling on the public transport network. It is vital that the transport network is only used by critical workers.

“As we work through these issues with our supply chain, consideration will be given to the impact on workers, particularly those who are on low incomes.”

The decision will add to confusion across the industry about whether sites must be closed or kept open.

This morning housing minister Robert Jenrick tweeted: “Advice for the housing, construction and building maintenance industries: If you can work from home, do so.

“If you are working on site, you can continue to do so. But follow Public Health England guidance on social distancing.“