The top EU official gave Theresa May until December 31 2020 to change her mind on Britain’s departure from the Brussels club, and said that the the EU would reconsider its red lines if the UK were to alter its position.
Speaking to European reporters, Mr Barnier said: “If the British wish to modify their red lines, we will modify ours in consequence.
“I am not hearing that today but everything is possible, there is no dogmatism.”
“So long as they have not left, during the transition period, everything is still possible.”
Mr Barnier added: “What creates the problem in Ireland, is the decision of the United Kingdom to leave the EU but also to leave what it is not obligatory to leave, that’s to say the single market and the customs union.”
Another diplomat also stated that the EU’s decision to leave open the option of changing its Brexit rules “is about being helpful, if, as many capitals hope, reality dawns and red lines disappear.”
But Mrs May repeated her ‘red lines’ in her Brexit speech in March, stating that the UK will leave the single market and customs union as well as the jurisdiction of the European Court of Justice.
Iain Duncan Smith also slammed Mr Barnier, saying: “Whatever he thinks is irrelevant – we’re leaving on March 29th next year.
“The UK has chosen quite categorically to leave the single market and the customs union.
“It would do Barnier and the rest of the Commission a lot of good to stop trying to interfere in UK democratic processes.
“Instead they should get on and do their damn job and do what he’s supposed to do, which is to make a good arrangement for both the UK and the EU.”
Remainer Labour MP Chris Leslie, a supporter of the Open Britain campaign, however said: “These comments by Michel Barnier demonstrate yet again how ludicrous it was for the Government to take single market membership off the table in the Brexit negotiations.”
The UK is set to formally leave the EU on March 29 2019, two years after the invocation of Article 50, but will remain in the single market and customs union for the whole transition period.
The 21-month transition period is due to end on December 31 the following year, coinciding with the end of the EU’s seven-year budget.
The UK will at this point be free to implement its own trade arrangements and immigration policies.
David Davis, the UK’s Brexit Secretary, has also stated the UK will be able to “get pretty substantively close” to achieving a free-trade agreement with the EU by October of this year.