The EUs chief Brexit negotiator has insisted that his team are ready to start divorce talks with the UK, calling for the parties to keep calm and negotiate.

Michel Barnier made the reference to the famous British Second World War Two poster – Keep Calm and Carry On – as he spoke in Brussels on Tuesday morning (6 December).

We are entering uncharted waters, he warned. The work will be legally complex, politically sensitive and it will have important consequences for our economies and people on both sides of the [English] Channel.

The French politician called for an orderly withdrawal and said he had used the past two months since his appointment to prepare for complex negotiations with the UK.

Barnier has so far visited 18 of 28 EU nations ahead of the talks and hopes to complete his tour of the remaining 27 states by the end of January 2017.

The 65-year-old, who heads up the European Commissions 30-strong Brexit taskforce, said he expected formal negotiations to last less than 18 months once the UK government has triggered Article 50, the official mechanism to split from the EU.

Prime Minister Theresa May has promised to make the move by March 2017, but was dealt a blow when the High Court ruled in November that MPs should have a vote on the issue.

The government is appealing the decision at the Supreme Court, with a final ruling expected in January.

Labour leader Jeremy Corbyn, meanwhile, has promised to table an amendment to any Article 50 bill, which could delay the Brexit process.

Barnier stressed that the UK could not cherry pick when it came to access to the EUs single-market after British ministers said they would seek to curbs to immigration.

Read more: IBTimes UK interviews the EU Parliaments chief Brexit negotiator

Freedom of movement is one of the blocs four key principles, including the free movement of goods, services and capital.

Immigration become a hot topic in the UKs EU referendum, with Vote Leave endorsing an Australian-style points based visa system. May has since ruled out such a system.

Elsewhere, Barnier said he hoped to complete negotiations with the UK by October 2018 and ratify the deal in March 2019.