Transport for London leaders are encouraging contractors to allocate shifts starting and finishing around busy travel times (06:00 to 08:00 and 16:00 to 17:30) to workers who can walk or cycle to and from work.

But Unite warned that many workers will have round trips of over 15 miles into central London and expecting them to cycle long distances during the winter “in the dark and in bad weather is a recipe for serious accidents.”

The union added that fatigue will be a danger for workers “expected to cycle home after undertaking a physically demanding 10 plus hour shift.”

Unite national officer for construction Jerry Swain said: “It needs to be remembered that construction workers are not pariahs and should not be treated as such. They are going to work as the government has decided that this is appropriate and necessary.

“Unite remains highly concerned that there is an attempt to force workers onto bikes and expect them to cycle long distances in the dark and in winter weather, undertake a long shift and return home again. This is a recipe for tragedy and should not be encouraged.

“It is essential that construction workers are able to socially distance from when they leave home, until when they return home again at night.

“Workers will not avoid congested trains unless they know that if they are late they will not be penalised or victimised, which currently occurs all too frequently on sites.

“The safety of construction workers is Unite’s key priority and the union is committed to working with contractors, construction clients, TfL and the Mayor of London to ensure the safety of construction workers while traveling to and from work.”