EU leaders are already holding talks about Britain's post-Brexit deal – despite Brussels banning negotiations until the UK formally announces it will quit.

Foreign Secretary Philip Hammond revealed top ministers are sticking two fingers up at the EU by holding private chats about the UK's future relationship with Europe.

Rules bar negotiations about Britain's withdrawal deal until the Government formally triggers Article 50 – the mechanism used to leave the bloc.

But Mr Hammond revealed talks were already underway, with the weekend's Nato summit overshadowed by the shock referendum result.

“Of course we discuss all the time in bilateral discussions with partners ... in the margins to reassure and try to explore the art of what is possible,” he admitted ​today.

“The EU will expect to negotiate with the UK and the EU is clear that it will not start negotiations, formal or informal, until an Article 50 notice has been served.

“But I don't think anyone is pretending that means that bilaterally we won't be discussing all of these issues with member states.

“It's probably not an exaggeration to say there is almost no other subject on the table when I get together with my colleagues.

“We are at a Nato meeting but most of the discussions have not been about Nato, they've been about the outcome of the referendum and the consequences of that.”

British leaders were “smelling the atmosphere” and finding out “what is the mood” as they talk with foreign counterparts, he claimed.

“Whatever noises maybe coming from Brussels – quite strident nosies – that is not the mood in their national capitals,” he rapped.

Fears have been raised over whether EU nationals living in the UK can stay once Britain quits.

Some campaigners want guarantees Brits living abroad can stay in their adopted homes before agreeing the same rights for EU citizens based in Britain.

Mr Hammond said: “We would be ready to have an early discussion about EU nationals to ensure that people who are established in the UK can be reassured of their ability to carry on with their lives.

“We absolutely understand that there are a lot of people who have become nervous and concerned - both British people living in the EU and Europeans living in the UK.”

But it would be a “dereliction of duty” to say EU nationals could stay in Britain before striking a deal for UK nationals to continue living abroad, insisted Mr Hammond.