The EU’s chief Brexit negotiator Michel Barnier has tested positive for coronavirus.

Mr Barnier's illness is the latest setback to hit talks which must be concluded by the end of 2020 if the UK is to avoid a no-deal Brexit on disadvantageous World Trade Organisation terms.

But Downing Street said Boris Johnson had no plans to ditch his self-imposed 31 December deadline and ask for an extension to negotiations on a UK/EU trade deal.

"We would of course send Michel Barnier our best wishes for his recovery," said a UK government spokesman.

"In relation to Brexit negotiations, we have been in close conversations with the EU about looking at ways to continue progressing the negotiations. Both sides have shared their texts of a potential legal agreement."

In a social media post, Mr Barnier said: “I would like to inform you that I have tested positive for Covid-19. I’m fine, morale is good. I naturally follow all the instructions, just like my team.

“For all those affected already, and for all those currently in isolation, we will get through this together."

A round of face-to-face Brexit trade talks due to take place in London this week were cancelled at the last minute because of the virus. The capital is thought to be the epicentre of infection in the UK.

Proposals to carry out the negotiations via videoconferencing did not go ahead, it is understood, because they would have still required groups of negotiators to gather to be practical. Over 200 officials, including both sides, are working on hashing out the agreement.

The last direct contact between Mr Barnier and the UK's chief negotiator David Frost is understood to have been the first negotiating round in the first week of March, which took place in Brussels.

Most staff on Mr Barnier's team have already been working from home since last week, in line with the rest of the European Commission. However, some, who have worked closely with him in recent days, have gone into self-isolation.

Mr Barnier, who is 69 years old, posted a personal video message to social media from self-isolation.

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(Photo by ISABEL INFANTES / AFP) (Photo by ISABEL INFANTES/AFP via Getty Images) ISABEL INFANTES AFP via Getty Brexit celebrations in Parliament Square Brexit supporters gather in Parliament Square, London, as the UK prepares to leave the European Union after 47 years. PA Photo. Picture date: Friday January 31, 2020. See PA story POLITICS Brexit. Photo credit should read: Jonathan Brady/PA Wire Jonathan Brady PA Brexit celebrations in Parliament Square LONDON, ENGLAND - JANUARY 31: Pro Brexit supporters gather ahead of the Brexit Day Celebration Party hosted by Leave Means Leave at Parliament Square on January 31, 2020 in London, England. At 11.00pm on Friday 31st January the UK and Northern Ireland exits the European Union, 188 weeks after the referendum on June 23rd, 2016. (Photo by Jeff J Mitchell/Getty Images) Leon Neal Getty Brexit celebrations in Parliament Square People draped in UK flags walks across Parliament Square during a rainfall in London, Friday, Jan. 31, 2020. Britain officially leaves the European Union on Friday after a debilitating political period that has bitterly divided the nation since the 2016 Brexit referendum. (AP Photo/Kirsty Wigglesworth) Kirsty Wigglesworth AP Brexit celebrations in Parliament Square LONDON, ENGLAND - JANUARY 31: Pro Brexit supporters gather ahead of the Brexit Day Celebration Party hosted by Leave Means Leave at Parliament Square on January 31, 2020 in London, England. At 11.00pm on Friday 31st January the UK and Northern Ireland exits the European Union, 188 weeks after the referendum on June 23rd, 2016. 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Both Belgium, where the European Commission is based, and Mr Barnier's native France, where he was located when he was taken ill, have implemented strict social distancing measures – though the UK has taken a softer-touch approach.

Both sides exchanged proposed legal texts for their free trade agreement at the start of this week, with the EU publishing its version and the UK giving its to Brussels in "confidence".