'˜We won't rubber stamp UK deal'

The Prime Minister was told there was no guarantee that measures would make it through the European Parliament unchanged, with one MEP warning it was a “distinct possibility” that the plans could face a “very hostile” reception.

Mr Cameron held a series of meetings with key players in Brussels in an effort to keep his proposed deal on track ahead of the gathering of European Union leaders on Thursday and Friday.

If a deal is reached, MEPs will eventually have to approve parts of the reform package, including restrictions on benefits, but Downing Street has insisted any agreement would be a “legally binding document under international law, entered into by the 28 leaders of member states” and that the European Parliament should deliver on that.

The parliament would begin the legislative process as soon as the UK voted to remain in the EU, the parliament’s president Martin Schulz indicated.

Mr Schulz said that once a deal is struck “there will be a very constructive debate” among MEPs.

“But to be quite clear: No government can go to a parliament and say: ‘This is our proposal, can you give a guarantee about the result?’ This is, in a democracy, not possible.

“Therefore my answer is the European Parliament will do the utmost to support compromise and a fair deal, but I can’t pre-empt the result in the European Parliament.

“But, once more, once the institutions agree, our experience is it goes in a good direction.”

Hungarian MEP Gyorgy Schopflin warned that the European Parliament could cause problems for the deal.

Asked if MEPs could “wreak havoc”, he said: “I think that’s a distinct possibility. That depends on the shape and concept of the deal - we won’t know this until the early hours of Friday morning.

“But I think the European Parliament will obviously look at it very closely and there will be some groups - I suspect the Greens - who will be very hostile to it indeed, unless it is pointing towards more integration, which I don’t see happening.”

Ukip leader and MEP Nigel Farage said: “There are many groups here who are spoiling for a fight.”

Britain’s renegotiation is the first item on the agenda for the European Council summit, but the gathering of 28 EU leaders is not scheduled to conclude until Friday lunchtime, after which Mr Cameron will call an immediate Cabinet meeting if he secures a deal. The meeting will effectively fire the starting gun on the referendum battle, as Eurosceptic ministers will be given the green light to campaign for a Leave vote in the poll expected on June 23.

Downing Street said the meetings with senior MEPs in Brussels had been “useful”. Mr Cameron spoke to key ally Mark Rutte by telephone and the Dutch Prime Minister agreed there was a “good basis for a deal”, Downing Street said.

European Council president Donald Tusk, who was in Prague for talks with Mr Sobotka, confirmed that EU citizens currently working in the UK would not be affected by the proposed curbs on in-work benefits. He said “unsolved problems” remained and there was “an extra mile” to go before reaching an agreement, with the “V4” Visegrad countries - the Czech Republic, Hungary, Poland and Slovakia - having concerns.