DAVID Cameron last night postponed plans to deliver a stark warning to the European Union that unless it sorts out its three key challenges then Britain will leave.

The Prime Minister had planned to tackle the EU over the eurozone crisis, its lack of competitiveness in the global economy and its democratic deficit today in a landmark speech in Amsterdam.

However, he cancelled it as the hostage situation involving British oil workers in Algeria deteriorated.

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The Prime Minister planned to use his address, marked by "urgency and frankness", to warn the EU it must change to deliver prosperity to its people and retain their support.

In pre-released extracts Mr Cameron did not mention the r-word – referendum – but hedid talk about "a duty" to act on the concerns of frustrated Britons.

He made it clear that Europe could not afford to shy away from its main challenges and must tackle them head on.

He said: "Why raise fundamental questions about the future of Europe when Europe is already in the midst of a deep crisis? Why raise questions aboutBritain's role when support in Britain is already so thin? There are always voices saying 'don't ask the difficult questions'. But it's essential for Europe – and for Britain – that we do."

The Prime Minister has faced mounting pressure from all sides over the eagerly anticipated speech.

Both his Liberal Democrat Coalition partners and Labour have warned "years of paralysing debate" would cost jobs.

On the other side of the argument, the Eurosceptic Right has urged Mr Cameron to give voters a say on EU membership.

Mr Cameron was due to use the speech to argue the problems in the eurozone are already driving fundamental change in Europe.

He intended to warn of a crisis of European competitiveness as other nations soar ahead and of a gap in democratic accountability between the EU and its citizens.

"If we don't address these challenges, the danger is Europe will fail and the British people will drift towards the exit," he was due to say.

"I do not want that to happen. I want the European Union to be a success and I want a relationship between Britain and the EU that keeps us in it. That is why I am here today: To acknowledge the nature of the challenges we face.

"To set out how I believe the European Union should respond to them. And to explain what I want to achieve for Britain and its place within the European Union."

The speech is unlikely to satisfy either faction in the debate.

Yesterday, LibDem Deputy Prime Minister Nick Clegg warned: "Having years of paralysing debate of if we're in or out of(Europe) is damaging."

However, Eurosceptics in the City of London called on the Prime Minister to offer Britain "a clear choice".

Mr Cameron is also under pressure from backbenchers from across his party, including a number of former Cabinet ministers. Liam Fox, the former Defence Secretary, called for British voters to eventually be given a "clear in/out choice".

In contrast, 25 Conservative MPs, including former foreign secretary Sir Malcolm Rifkind, urged him to use his speech to emphasise Britain is better off in the EU.