Tuesday 6 December 2016 1:37 pm

EU negotiator Michel Barnier has given Britain 18 months to reach a Brexit deal

One of the EU's top officials has warned the the British government it must reach a deal on Brexit within 18 months of activating Article 50.

Michel Barnier, who will lead talks with the UK on behalf of  the European Commission, said today it was "the sooner the better" for Prime Minister Theresa May to launch negotiations.

"Time will be very short. It's clear that the period of actual negotiation will be shorter than two years," Barnier said, adding that up to six months could be needed for member-states to ratify a deal with the UK.

Read More: Does it matter if the government loses the Supreme Court Article 50 case?

Article 50 provides the UK with two years to establish a new relationship with the EU before it is expected to default to World Trade Organisation tariffs. Downing Street said today it did not want to extend talks beyond that time frame.

Barnier summed up his message to London with a pithy "keep calm and negotiate", and warned that a "very limited transition" deal is possible, but only after British officials have indicated more on the type of relationship they wish to establish with the EU.

Read More: "Posturing" Euro chief Dijsselbloem issues London warning

His comments came as part of a hardening of the rhetoric towards the UK, with Eurogroup chairman Jeroen Dijsselbloem also warning the UK's attitude was making a smooth transition to a new relationship more difficult.

Speaking ahead of a meeting of EU finance ministers, including chancellor Philip Hammond, Dijsselbloem said: "It can be smooth and it can be orderly but I think it requires a different attitude on the part of the British government because the things that I've been hearing so far are incompatible with smooth, incompatible with orderly."