David Cameron's promise to hold a referendum on Britain's membership of the European Union within the next five years, regardless of the state of negotiations over a revised EU Treaty, is playing with fire. He can control neither the timing nor the outcome of the negotiations, and in so doing is raising false expectations that can never be met and jeopardising both Britain's long-term interests and the unity of the EU.

The speech itself contained something for everyone, as its main purpose was to unite his own party on the issue of Europe. But it was full of inconsistencies.

Strength in numbers

He claims to want a common set of rules for the Single Market at the same time as wanting exceptions for Britain. He wants a Single Market Council to focus on raising competitiveness, but we already have one. He wants a global response to terrorism but aims to withdraw the UK from co-operation on justice and police work. He claims that Europe just offers more of the same and never changes; but the EU is constantly changing and adapting to circumstances.

I expect more integration will be necessary - at least within the Eurozone - in the years ahead as a response to the debt and banking crisis. It is the Conservative Party's 'conservative' attitude to Europe that perhaps needs to change, and instead recognise that in the 21st century Member States wield greater influence by sticking and acting together.

Seeking unilateral renegotiation or repatriation of existing powers would threaten the integrity of the Single Market and risks precipitating a free-for all as other countries seek concessions to suit their own national interests. Cameron will not succeed if he attempts to hold his European partners to ransom.

The real problem for Cameron is the internal rift within his own party and the pressure from Ukip. He seems to be jeopardising the interests of his country for internal party stability. Britain has suffered over the years from the chronic failure of politicians to make a positive case for Europe and counter the untruths in much of the populist press. He did make an attempt at this in sections of the speech, suggesting that it was not his vision to see Britain isolated in the world.

Contradicting himself

But by promising to effectively pull Britain out of the EU unless he can repatriate powers he contradicts his own intentions and creates more, not less, uncertainty about Britain's future.

The one positive effect of the speech is the genuine debate that is finally taking place about the EU and Britain's place in it. Business leaders and US diplomats have lately decided to speak out publicly, so worried are they by the prospects of Britain cutting itself off from the world's largest trading bloc.

I favour a more efficient European Union, with enhanced capability to act on the global stage - including co-ordinating responses to conflict and terror threats in our neighbourhood. Britain has been and surely will continue to be a key part of that - but only if it remains a full member of the club.

Guy Verhofstadt was Prime Minister of Belgium from 1999 to 2008. He is President of the Group of Liberals and Democrats in the European Parliament