DAVID Cameron will take his EU reform charm offensive to Germany on Friday as campaigners warned that any watering down of his draft proposals would be “playing with fire”.

The Prime Minister will have private talks with Europe’s powerbroker, Chancellor Angela Merkel, before giving a keynote speech at the annual St Matthew’s Banquet in Hamburg, where he will, said No 10, made the "wider case" for reforming the EU.

It will mark the start of the final push towards seeking a deal at the European Council summit in Brussels next week.

On Tuesday, Mr Cameron will be in the Belgian capital to meet the leaders of the different political groupings to secure their support.

Forty eight hours later, he will return to Brussels for the summit when the UK Government hopes to secure the backing of all other 27 member states, paving the way for an in-out referendum on June 23.

However, the deal has not yet been done. Earlier this week, Donald Tusk, President of the European Council, described the process as “fragile” and said he had cleared his diary to focus on the negotiations.

Philip Hammond, the Foreign Secretary, said there were still some outstanding issues to resolve, explaining: “Some of which have been addressed - language issues - in the latest iteration of the draft, some of which have not been addressed.

"So the discussions continue and I do not think it is sensible to draw any conclusions about the shape of the deal until we see the final text that emerges from the European Council meeting."

The proposed reforms have been amended in response to concerns of some member states.

The new draft text being discussed in Brussels includes changes which would effectively limit the use of the proposed emergency brake on providing benefits to migrant workers in the UK and a handful of other member states.

The revised document produced by Mr Tusk contains new language apparently designed to assert the point that the UK's distaste for ever-closer union is not universal.

Downing Street sources played down the significance of what they said were "relatively minor technical changes," that left the substance of the draft deal "unchanged".

Eurosceptic MP Steve Baker, co-chairman of Conservatives for Britain, said: "The Prime Minister is asking for very little in this renegotiation but now the EU is watering it down even further.

"Worse still, the proposed deal now contains hidden nasties that will be used to undermine British interests. A Remain vote will be a green light for more money and power flowing to Brussels with Britain helpless to stop it. The only safe option is to vote Leave."

Stephen Booth, co-director of think-tank Open Europe, added: "EU leaders are playing with fire if the proposed deal is watered down as it would make the package a very hard sell in the referendum campaign."

Elsewhere, Hilary Benn, the foreign shadow secretary, issued an impassioned plea for the UK to vote to remain in the EU, saying the case was "stronger than ever" and that Brexit would be exploited as "weakness" by Russian president Vladimir Putin.

He also argued that campaigners for Scottish independence would also take the opportunity to "have another go" at breaking up the Union if Brexit happened.