TRUCK queues at Dover and “disruption” to air traffic were scenarios set out by the EU’s chief negotiator yesterday as he warned of “serious consequences for everyone” if Britain and the EU fail to reach a Brexit deal.

In a wide-ranging speech ahead of Article 50 talks, Michel Barnier told the UK Government it must agree “principles for an orderly withdrawal” before trade talks, including those relating to how much money it owed the bloc, as well as settle the rights of millions of EU citizens living in the UK and British citizens in the EU.

The former French government minister said the negotiations he will lead will be transparent and open, saying “they cannot take place in secret”.

He said his priority at the outset would be to end uncertainty for EU and British nationals living on the opposing territories, saying his watchword would be “citizens first” before turning to the issue of financial dues.

He insisted Britain will face no punishment for leaving, but that “we must settle the accounts”. Some estimates suggest the EU wants Britain to pay a divorce bill of up to €60 billion (£52bn) to cover EU staff pensions and other expenses the UK has committed to. The UK Government has not ruled out paying but is expected to contest the bill.

At a plenary session of the European Committee of the Regions in Brussels, Barnier said: “Each country must honour its commitments to each other.

“When a country leaves the union, there is no punishment. There is no price to pay to leave. But we must settle the accounts. We will not ask the British to pay a single euro for something they have not agreed to as a member.

“In the same way, the 27 will also honour their commitments concerning the United Kingdom, its citizens, companies and regions. This is the mutually responsible way to act.

“If I may quote one of the greatest men of European history, Winston Churchill: ‘The price of greatness is responsibility.’ That is true for Britain and for us.”

Brushing aside one of Theresa May’s red lines over the future role of European judges, he stated the EU’s demand that interim measures “will be within the framework of European law” and the European Court of Justice. Such a transition could not allow Britain to pick and choose access to areas of the single market.

Tackling May’s assertion that “no deal is better than a bad deal”, he set out a bleak vision of the “serious consequences” from no agreement.

“More than four million British citizens in the EU and European citizens in the UK faced with complete uncertainty about their rights and their future, the reintroduction of binding customs controls, which will inevitably slow down trade and lead to queues of trucks at Dover, serious disruption to air traffic, an overnight suspension in the movement of nuclear materials to the UK,” he said.

He said: “A no-deal scenario is not our goal. We want an agreement. We want to succeed.” May is set to trigger the two-year period of negotiations on March 29, and the talks could start in May.

Kirsty Hughes, director of the think tank the Scottish Centre on European Relations, which launched yesterday, said the negotiations would be challenging and could break down.

“There is a significant possibility of breakdown, though it is more likely there will be a deal,” she said. “You might get periods when negotiations stall. It may get most tense near the end of September 2018 or we could see the biggest row at the beginning.

“You have Boris Johnson banging on about WTO being fine, but I don’t think that is really how May looks at it.”