Whitehall mandarins branded the Frenchman’s comments “irrational and stupid” and said they “need calling out” following his outburst in Berlin.
Addressing the Berlin Security Conference this morning Mr Barnier pointed out that Europe has faced a number of devastating terror attacks in recent years.
But he said that rather than sticking around to help out Britain had “chosen to be on its own” and leave the club.
He scolded: “Never had the need to be together, to protect ourselves together, to act together been so strong, so manifest. Yet rather than stay shoulder to shoulder with the Union, the British chose to be on their own again.”
British officials reacted with fury to the remarks, with one telling Politico they amount to the EU “accusing us of ducking out of the fight agaist Daesh”.
A third raged raged that the comments were “ignorant, inflammatory and irresponsible so close to sensitive negotiations”.
In a speech that with will raise eyebrows over its abrasiveness Mr Barnier warned that Britain will have to leave the European Defence Agency and Europol as a “consequence” of Brexit.
Mr Barnier said that there would be “appropriate legal and operational conclusions” from Brexit and that Britain will “lose its decision-making powers at the European level and some levers for wielding influence”.
On top of that, he added that in future Britain “will not be able to take command of EU–led operations or lead EU battlegroups” not will it be a member of the European Defence Agency or Europe police force.
He said this will mean the UK defence secretary no longer taking part in meetings about EU military matters and UK ambassadors also being booted off its security committee.
The Frenchman explained: “Everything I have just said is the logical consequence of the sovereign choice made by the British. We regret this vote. But we respect the choice that has been made.”
However, he also called for an “ambitious” partnership with post-Brexit Britain including wide-ranging cooperation on defence, with the bloc pressing ahead with plans for its own army.
Mr Barnier said much cooperation between the EU and UK on defence and security matters would continue both at country to country level and through membership of NATO.
And he praised Theresa May’s “unconditional” promise to maintaining European security, saying: “History teaches us that there must be no horse-trading over the security of Europeans – that is an absolute necessity.”
In a discussion paper earlier this year the Government put forward proposals for an ambitious partnership between the EU and UK on the issues of security and defence in the future.
Ministers left open the option of Britain contributing to European military initiatives, such as its planned £5 billion a year defence fund, as a way of ensuring good post-Brexit cooperation in the fight against terror.