David Cameron will today reject insist that his EU renegotiation plan is not “mission impossible”.

The Prime Minister will set out his 'shopping list' of reforms in a letter to the President of the European Council, Donald Tusk.

Yesterday he warned that he could back a UK exit if his demands were not met.

But in a speech today he will strike a more optimistic note, saying that he did not believe "for a minute" it was impossible to reach an agreement.

His four key objectives are protecting the single market, writing competitiveness “into the DNA” of the EU, exempting Britain from an “ever closer union” – bolstering national parliaments, and tackling abuses in the right to free movement.

He will say: “There will be those who say – here and elsewhere in the EU – that we are embarked on Mission Impossible.

“I say: why?

“I do not deny that seeking changes which require the agreement of 27 other democracies, all with their own concerns, is a big task.

“But an impossible one?

“I do not believe so for a minute.”

Yesterday Mr Cameron was forced to deny watering down his demands, insisting he was "deadly serious" about the need for reform.

And he reiterated his call for EU migrants to be barred from claiming tax credits and child benefit until they have lived in the UK for at least four years.

A No 10 source said that Mr Cameron believes that "Britain could survive outside the EU, the question and the judgment is whether we would be more successful or not".

Shadow foreign secretary Hilary Benn said that political leaders had to make the case for the EU.

He said: "It is important that the way in which the European Union works changes to reflect a changing world and Britain's priorities.

"But we also have to say clearly that Britain is stronger and more successful because we are part of the EU."

The Scottish National Party accused Mr Cameron of moving Scotland and the rest of the UK closer to the EU exit door.

Stephen Gethins, the SNP's Europe spokesman , who will today lead a debate at Westminster on the role of devolved administrations in EU renegotiations, said: "David Cameron has been playing with fire in his EU referendum dealings from day one – and his latest moves, suggesting he is prepared to argue for an ‘out’ vote, have moved Scotland and the UK closer to the European exit door than ever before."

Meanwhile, Dutch prime minister Mark Rutte warned that leaving the EU would be a "killer" for the City of London and leave the UK as a "mid-sized economy" in the mid-Atlantic.