EU referendum: David Cameron admits he does not know how migrant benefits system would work

David Cameron has admitted after weeks of intense negotiations to secure an EU reform deal in Brussels that he still does not know of how an “emergency brake” on migrant benefits would be implemented.

Speaking on the BBC’s Andrew Marr Show in his first major interview to put the case for staying in the EU, the Prime Minister said the UK would be “stronger, safer and better off” if it votes to remain.

But when pressed on the details of the deal he has secured with the rest of Europe, Mr Cameron admitted “we’re going to settle all that later”.

“What we do know is you get no benefits to start with and you don’t get full benefits for four years,” Mr Cameron said. “[We will have] no more something for nothing and people have to pay in before they get out. I think that is something people said we wouldn’t achieve and it is something we have achieved.”

Mr Marr asked if a Hungarian migrant would be entitled, for example, to 90 per cent of benefits after just six months, to which the Prime Minister was only able to say that the brake “is going to be phased in over four years”.

“Now we have to settle the details and put all that in place, which we will,” he said.

Mr Cameron was speaking ahead of an expected announcement from Boris Johnson later today, in which the London Mayor is to reveal whether he favours in or out.

Asked what he would say to convince Mr Johnson to join his side, the Prime Minister said he would say "the same thing I would say to anyone".

"I think the prospect of linking arms with George Galloway and Nigel Farage and leaping into the dark is wrong for this country," he said.

"If Boris and if others really care about being able to get things done in our world, then the EU is one of the ways in which we get them done."

On the question of sovereignty, Mr Cameron said leaving the EU would mean Britain lost the power to defend businesses against discrimination, receive security information from other European countries or fight trade regulations.

Leaving would give “the illusion of sovereignty – but you don’t have power, you don’t have control, you can’t get anything done”, he said.

“If you love this country – and I love this country so much – then you want what’s best for it, and you want to make sure we are stronger, we are safer, we are better off and we are able to get things done in the world,” he said.

Part of the deal secured with Brussels means that benefits claimants from other EU countries receive less money if they come from a poorer country - a bid to remove the incentive to come to Britain and receive more money for not working.

Asked if working out different levels of benefits for claimants from 27 different countries would be challenging for an already overstretched Department for Work and Pensions, Mr Cameron disagreed.

He said: “It’s not a difficult calculation, you just have to work out the relative cost of living in different countries and you pay that level of child benefit.”