Michel Barnier has said Britain could regain its special terms if it rejoined the EU and claimed it was becoming clearer every day to the British people that they would be stronger in Europe.

In an interview before the 10th anniversary of the Brexit referendum next week, the EU’s former chief Brexit negotiator said he could not see any obstacle to the UK keeping the pound and remaining outside the passport-free Schengen travel area should the country rejoin.

The comments cast serious doubt on suggestions from some authoritative voices, including Poland’s foreign minister, that the UK could be forced to accept more difficult terms on re-entering the bloc.

They will be seen as a boost to those who are campaigning for the UK to rejoin the EU, with polling showing that support for rejoining is stronger when the old terms are on the table.

Under the EU treaties, all member states are expected to join the euro, apart from Denmark, which has a permanent opt-out.

New member states are also legally obliged to join the Schengen passport-free area once they meet the necessary technical, legal and security requirements.

Barnier, who remains an influential voice in Brussels and was prime minister of France in 2024, said he believed the UK would be able to regain exemptions given the precedents already set.

He said: “I am speaking about Schengen, I am speaking about the single currency: there are other member states who are not in them. It is perfectly possible to have opt-outs in these fields.”

Five of the 13 countries that have joined the EU since 2004 are yet to join the single currency. The treaties do not specify a particular timetable for joining the euro area.

Ireland is the only EU member state with an official opt-out from the Schengen passport-free travel area.

Barnier, who continued as a Brexit adviser to the European Commission until his return to French politics, said he did not want to comment on whether the UK could also keep the rebate secured by Margaret Thatcher, which reduced the UK’s financial contributions to the bloc’s budget.

He said: “The DNA of the EU is solidarity that the more developed country helps the other … We will see if the UK decides to ask to join the EU. It will be a choice and it will be open to negotiation. I will be ready at that time for free advice.”

Barnier will be in London on Tuesday for a UK in a Changing Europe conference marking the decade since the Brexit vote. He spoke to the Guardian ahead of this week’s announcement that the next round of UK-EU “reset” talks will take place in Brussels on 22 July after several delays.

Senior EU diplomats have recently warned that “momentum is being lost” in the talks, with the UK resisting an EU call to restore lower pre-Brexit tuition fees for EU students as part of a youth exchange deal.

Barnier navigated four years of Brexit negotiations, which culminated in agreement on a trade deal in December 2020.

He said that he remained convinced that the UK had made the wrong choice in leaving the EU and that the evidence for that was becoming clearer “every day”.

With reference to the UK’s slow economic growth and toxic immigration debate, Barnier said: “It would not be fair to say that the problems of the UK today are due to Brexit but what I am sure of is that all these problems are more difficult because of Brexit.”

Barnier said the government’s hopes to build a closer economic relationship with Europe outside the EU remained problematic due to the rejection of the free movement of people.

With France facing the real prospect of a far-right president being elected next spring when Emmanuel Macron’s term ends, Barnier said the EU could not show any flexibility on facilitating frictionless trade for fear that other nationalists would seek the same.

“No,” he said, when asked whether a deeper trade relationship was possible given Keir Starmer’s red line on free movement. “Never give any argument to the far right in France or elsewhere.”

Asked if he believed the UK would rejoin the bloc within his lifetime, the 75-year-old said: “I don’t know the length of my life. I think day after day the British people will see in the current world, that it is more dangerous, more fragile, more unstable, that we cannot be alone. It is true for France, it is true for Germany, it is true for everyone. Every day it will be more clear.”

According to recent polling carried out by YouGov, 57% of Britons think the UK was wrong to vote to leave the EU, including 23% of leave voters.

The polling suggests that 55% of Britons support the UK rejoining the EU but that this falls to just 35% if the UK had to rejoin without its prior opt-outs, with 43% opposed.

Barnier, who is yet to announce his candidacy for the French presidency but who is thought to be manoeuvring to be a potential unity figure of the centre and centre right, said he believed the UK should join the EU member states, along with Ukraine and Norway, on a new European Council for Defence and Security.

The members would cooperate and potentially jointly borrow for military initiatives and those related to artificial intelligence and other disruptive technologies, he said. “It is my proposal to create this independently of the EU institutions,” he said.