It is an “illusion” to think that the process of Britain leaving the European Union will be quick or painless, the European Commission’s chief negotiator Michel Barnier has warned.

Mr Barnier was speaking on Wednesday as he set out the Commission’s detailed negotiating guidelines for the first phase of withdrawal talks, expected to begin in earnest after the June 8th general election.

Mr Barnier said there would be a focus on Ireland during the initial talks and he would travel to Dublin next week.

In a press conference in Brussels, Mr Barnier said that the first phase of negotiations would focus on the financial settlement, the status of expatriate citizens and the future border between the UK and EU in Ireland.

He insisted that the the so-called divorce bill was not a punishment of the UK for leaving, but simply a “settling of accounts”.

“The UK must put a great deal of energy and effort into these three issues over the next weeks and months and that will increase the chances of making a deal,” said Mr Barnier.

“Some have created the illusion that Brexit would have no material impact on our lives or that negotiations can be concluded quickly and painlessly. This is not the case.

“We need sound solutions, we need legal precision and this will take time.”

His comments came as news reports suggested that the Commission may present the UK with a €100 billion euro “divorce bill”, sharply increased from the previous estimates of €60 billion.

But Brexit secretary David Davis rejected suggestions that the UK will foot a bill on that scale, saying Brussels will only receive what it is legally owed.

Mr Davis also dismissed as “laughable” reports that prime minister Theresa May would be barred from negotiating with her counterparts.

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Mr Barnier said the financial withdrawal agreement was not a punishment or an exit bill, but a settling of accounts.

He said the UK would have to “close the account” in a “single financial settlement” which “will cover all the financial relations between the United Kingdom and the European Union. All the commitments entered into as a member of the union”.

Mr Barnier said: “Now, this is not a punishment, nor is it an exit tax of some kind. The union and the United Kingdom have mutual commitments. They have committed to financing projects and programmes together. We decided these programmes together. We benefit from them together, and we finance them together.

“Basically, we have to close the account, and it is no more and no less. No punishment. There is no Brexit bill.”

Mr Barnier declined to put a figure on the expected size of the exit bill, but fiercely rejected suggestions that Brussels was demanding a “blank cheque” from London.

“I cannot accept the term ‘blank cheque’,” he said. “There was never any question of asking the UK to give us a blank cheque. That would not be serious.

“All we are asking for is for accounts to be cleared, for the honouring of commitments which the UK has entered into.

“It’s not a blank cheque. We know exactly what we are speaking about and what we are going to discuss. But you cannot count on me to give you any figures, because they will develop.

“As far as I’m concerned, leaving the Union does not have a price which will have to be paid. We have an orderly withdrawal with accounts to be cleared.”

Mr Barnier attended last week’s Downing Street dinner with Mrs May and Jean-Claude Juncker following which the Commission president reportedly remarked that the prime minister was “in a different galaxy” on Brexit.

Characterising the meeting as “cordial”, Mr Barnier said he hoped to build “an entente cordiale” between the UK and EU “which will last well beyond Brexit”.

“Of course the positions between us are different — sometimes very different,” he said. “That is no surprise to anyone. That is why we need negotiations and why we have to start these negotiations as soon as possible.”

The EU was ready to start substantive talks “as soon as the UK is ready to come to the table”, he said. There had been 10 months of uncertainty and it was “high time” to start negotiations because “the clock is ticking”.

Mr Barnier said last week’s dinner was the first time he had met Mrs May and was an opportunity for them to discuss their “shared passion” of rambling and hiking in the mountains.

And in a barely-veiled warning to the prime minister, he drew a parallel between the perils of mountain-walking and the negotiations ahead of her.

“If you like walking in the mountains, you have to learn a certain number of rules,” said Mr Barnier.

“You have to learn to put one foot in front of the other, because sometimes you are on a steep and rocky path. You also have to look at what accidents might befall you — falling rocks. You have to be very careful to keep your breath, you have to have stamina because it could be a lengthy path. And you have to keep looking at the summit, the outcome. That’s what I learnt when mountain-walking.”

Mr Barnier said he hoped to be in a position by October or November this year to reach a judgment on whether sufficient progress has been made in withdrawal negotiations to trigger the start of the next phase, involving talks on future trade arrangements.

In order to move to the next phase, the EU would need “clear commitments”, rather than “window dressing” from the UK on the financial settlement, expatriates’ rights and borders.

This would involve final agreements on issues like the cut-off date for EU citizens to retain rights in the UK, and the nature and duration of those rights, as well as a “specific methodology” for calculating the UK’s liabilities, he said. And it will have to be clear that issues like these cannot be “reopened”.

PA