A London Underground tube driver has reportedly tested positive for coronavirus.

The man, who works on the Jubilee Line, has been self-isolating this week after returning from holiday in Vietnam, sources told PA.

An internal message to staff said the driver, based at the North Greenwich depot, had tested positive for Covid-19.

"The operator is receiving support from health services and is continuing to follow Public Health England (PHE) advice to self-isolate.

"The train operator has recently returned from a trip abroad, where it is thought the illness may have been contracted," said the memo.

A Transport for London (TfL) spokesman said the driver was receiving support from health services, adding that he was not working in a customer-facing area.

"The safety of our staff and customers is our top priority and we are taking all necessary precautions.

"The areas where the driver worked are being cleaned, including the depot and the trains, in line with guidance from Public Health England with whom we are working closely."

Rail union leaders wrote to Transport Secretary Grand Shapps on Thursday, voicing concern about what advice transport workers are being given.

The letter said: "We are writing jointly as representatives of workers in the transport industry to implore you to break your silence and give leadership on measures that public transport can take to tackle coronavirus.

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"Transport workers are receiving different advice from different companies - and in some cases even within the same company - about what actions to take in the event of suspected or actual illness.

"There is concern of 'over-managing' attendance procedures and how they are being applied. Clearly, if someone is told to self-isolate they should not then be penalised by their employer for doing so in the interest of public health, yet this is currently the case in the rail and bus industries.

"Our privatised transport system is not conducive to swift and co-ordinated responses. There is apparently no consistency across the public transport network in how transport workers will be treated if they fall ill.

"Companies where employees work side by side with transport workers employed by another company are being treated differently, leading to confusion and frustration."

Finn Brennan, Aslef's organiser on London Underground, said: "Many people will be concerned about family members who may be at high risk because of their age or underlying health conditions."

Mick Whelan, general secretary of Aslef, said: "We have written to management demanding an emergency summit to discuss TfL's response to this public heath crisis."

The news comes as TfL reports a small drop in the number of people using the London Underground amid growing concern about the coronavirus outbreak.

The decline may be partly due to more people working from home, according to the transport body.

A spokesperson said: "The overwhelming majority of Londoners are using our services as normal in line with the Public Health England advice that there is no specific concern about public transport.

"We have seen a small reduction in ridership over the last week. This may reflect some of the pre-emptive action taken by some employers around coronavirus, but passenger ridership is affected by a range of factors including fluctuations in the economy and extended periods of bad weather."