Michel Barnier, the EU's former chief Brexit negotiator, says the UK could regain its special terms if it rejoins the bloc again. 

Ahead of the 10th anniversary of the Brexit referendum, June 23, Barnier said he could not see any reason for the UK not to keep the pound and remain outside the passport-free Schengen Zone, were the country to rejoin the EU. 

He told the Guardian: '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.'

Current EU law states that all member states are expected to use the euro as their currency. The exception to this rule is Denmark, which has a permanent opt-out. 

But five of the 13 nations that have joined the EU since 2004 have not yet made the euro their currency. 

On top of this, the treaty does not specify a timetable for doing so. 

The issue of the Schengen Zone is trickier. New member states of the EU are legally obliged to join it. 

Only Ireland has an official opt-out from this part of EU membership. 

But Barnier, who continued to work as a Brexit adviser to the European Commission before he returned to French politics, 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 said it was becoming clearer 'every day' that the UK made the wrong choice back in 2016 by voting to leave the EU. 

Referring to a decade of poor growth and the increasingly toxic conversation around immigration, he 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.'

Asked whether he thought the UK would ever rejoin the EU in his lifetime, he carefully 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.'

Barnier, just a month after the UK formally voted to leave the EU, was named the bloc's chief negotiator. 

He dealt with multiple prime ministers, including Theresa May and Boris Johnson, as the UK and EU hashed out details of the formal Brexit deal.  

Barnier's intervention comes at a delicate time for the UK's relationship with the EU. 

The bloc is waiting with anticipation to see if Andy Burnham, Starmer's main challenger who has a significantly different view on Brexit to him, will win in Makerfield - opening up a path to Downing Street. 

Starmer, who is fighting for his political survival in the face of ​pressure from within his own party, has cast closer ​relations with the EU as a key part of efforts to deliver ‌economic ⁠growth and address the cost of living.

Starmer said this week that Britain and the EU will hold another summit in July as his government seeks to reset ties with the bloc and push for closer ​cooperation on trade, security and the economy.

'My Labour ​government is delivering on our promise to reset our ⁠relationship and put Britain at the heart of Europe,' ​Starmer said in a post on X.

'Together we will tackle ​the cost of living, boost jobs and create opportunities for young people.' 

Burnham, meanwhile, has been less keen on bringing the UK back into the EU. He said in mid-May that Britain would be stuck in 'a permanent rut if we’re just constantly arguing.'

He added: 'My view is that Brexit has been damaging, but I also believe the last thing we should do right now is rerun those arguments.'