Mr Barnier, the EU‘s chief negotiator, said he and his UK counterpart Lord Frost had ‘decided to suspend the negotiations at our level for a short period’ in the wake of the test result.
Lord Frost said he would remain in ‘close contact’ with Mr Barnier and insisted ‘the health of our teams comes first’.
A UK Government spokesman said ministers were now talking to Brussels about the ‘implications for the negotiations’.
The suspension of formal talks comes as the clock ticks ever closer to the end of the ‘standstill’ transition period in December with the two sides yet to agree a trade accord.
The positive test raises major questions about how and when face-to-face talks could resume because of the potential need for the negotiating teams to self-isolate.
Top-level Brexit trade talks between Michel Barnier and Lord Frost have been suspended after a member of the EU team tested positive for coronavirus
Lord Frost said he would remain in ‘close contact’ with Mr Barnier while the UK Government said it is speaking to EU officials about the implications for the talks
Mr Barnier tweeted: ‘Update: one of the negotiators in my team has tested positive for COVID-19. With David Frost we have decided to suspend the negotiations at our level for a short period. The teams will continue their work in full respect of guidelines.’
Mr Frost responded: ‘I am in close contact with Michel Barnier about the situation. The health of our teams comes first. I would like to thank the [European Commission] for their immediate help and support.’
A UK Government spokesman said: ‘The Commission has informed us that an official in their delegation has tested positive for Covid-19.
‘We are discussing with them the implications for the negotiations. We have been, and will continue to, act in line with public health guidelines and to ensure the health and welfare our teams.’
The two sides have been engaged in intensified talks in recent weeks, with negotiating rounds alternating between London and Brussels. The latest round of talks was taking place in the Belgian capital.
The hammer blow to negotiations came after European leaders demanded the EU publish its no deal Brexit contingency plans amid fears businesses on the continent will have little time to prepare if talks collapse.
Officials in Brussels had said overnight that trade negotiations between Britain and the bloc were now entering the ‘final push’.
But some EU member states are increasingly nervous because negotiating deadlines keep being missed and time is running out before the end of the transition period.
France, the Netherlands and Belgium are all pushing European Commission president Ursula von der Leyen to set out the EU’s worst case scenario plans so businesses have a ‘safety net’ and can start to prepare just in case trade talks fall apart.
The middle of November had been viewed as the latest a deal could be agreed between the UK and the EU because of the amount of time needed to ratify and implement the new arrangements.
Deadlock remains in a handful of crunch areas, including on post-Brexit fishing rights, and European leaders believe it is now time for the EU to spell out its contingency plans for a disorderly split.
A senior EU diplomat told The Times: ‘We must now come up with contingency measures.
‘January 1, 2021 is getting close; we need a safety net. Of course, this sends out a political signal.
‘But it is high time to prepare people and businesses in case we cannot fix an agreement in time. I know member states will ask to get contingency measures out into the open.’
Mr Barnier is said to be reluctant to publish the plans because of fears it could give Boris Johnson and the UK the upper hand in trade talks. The UK Government has already published its own no deal contingency plans.
EU leaders will this evening take part in a video summit to discuss the bloc’s response to the coronavirus crisis.
But they are also expected to be updated on the state of the trade talks which both sides now admit are heading down to the wire.
Ursula von der Leyen, the president of the European Commission, is under pressure from European leaders to publish the EU’s no deal Brexit contingency plans
Mr Barnier is said to be reluctant to release the contingency plans because of fears they could give Boris Johnson and the UK the upper hand in trade talks
Valdis Dombrovskis, a European Commission vice-president, said yesterday: ‘The negotiations are ongoing with great intensity because we are now in the final push to reach agreement.
‘There’s still substantial work to do.’
A failure to agree a deal before the end of the transition period will see the two sides forced to trade on World Trade Organisation terms from January 1 and that will mean tariffs being imposed on goods.
Business groups on both sides of the English Channel are calling for the EU and the UK to compromise and strike an accord as they continue to warn companies cannot afford a chaotic split, especially after they have been hammered by the coronavirus crisis.
It came as it emerged the UK and Canada are closing in on agreeing a post-Brexit continuity trade deal.
The Prime Minister’s Official Spokesman said: ‘As you are aware we are committed to securing a continuity trade deal with Canada before the end of the transition period.
‘Talks are at an advanced stage and are progressing well.’