Hans-Olaf Henkel said Mr Barnier and the European Parliament’s Brexit co-ordinator Guy Verhofstadt want to make sure the experience of withdrawal is such a “catastrophe” for the UK that no other country will follow it out of the EU.
Mr Henkel urged the UK to accept the jurisdiction of the European Court of Justice over civil nuclear issues to be able to remain in Euratom, and said he still hoped Britain’s political leaders might be ready to ask voters to think again about the “colossal mistake” of Brexit.
Euratom has been a key issue on the table in Brussels this week, along with the future status of EU nationals in the UK, borders and the Brexit “divorce bill”.
The financial settlement emerged as the major battleground on day two of the second round of formal exit negotiations, with Brussels thought to be demanding tens of billions of pounds but unwilling to set an exact figure.
It is understood that Britain will not agree a final figure for the so-called Brexit divorce bill until the 11th hour of its withdrawal process from the European Union.
There was frustration on both sides, with the EU irritated that the UK has not set out a clear position on what it believes are its financial obligations that will continue for a limited time after leaving the bloc.
Brexit Secretary David Davis has been in close touch with the UK team ahead of his return to Brussels on Thursday and a potential press conference with Mr Barnier.
Mr Henkel, a member of the small Liberal Conservative Reformers (LKR) party, who is deputy chairman of the Tories’ European Conservatives and Reformists (ECR) grouping in the European Parliament, said the EU must “accommodate” the UK, but warned it would require “give and take on both sides”.
Writing in The Times, he urged fellow MEPs not to listen to Mr Verhofstadt or Mr Barnier, who “want to make a mess out of this whole unhappy situation”.
Describing Mr Verhofstadt as “an ambitious politician who wants to achieve a United States of Europe”, Mr Henkel said the Belgian former prime minister’s attitude paved the way for the “disaster” of Brexit by allowing British Eurosceptics to whip up anti-EU sentiment.
“Mr Verhofstadt now wants to punish the British, full stop,” said the German MEP. “He says he doesn’t want to, but I’m afraid he does. My impression is that Mr Barnier wants to do the same.
“The reason is simple. They would seek to make sure that Brexit is such a catastrophe that no country dares to take the step of leaving the EU again.
“This is a terrible situation for us all.
“My position is that the EU must accommodate the British. It will require give and take on both sides. For you, it will mean paying in and abiding by the rules, as Britain does now, and accepting the jurisdiction of the European Court of Justice when it comes to overseeing Euratom.”
He added: “Is it too much to hope that leaders of stature in the UK might say to people that, when it comes to Euratom, they got it wrong? And who knows, as we all face the disaster of Brexit, perhaps when it comes to EU membership itself, tell the British people, ‘We’ve all made a colossal mistake’?”