David Cameron: It's not in our best interest to act rashly

We need to be utterly single-minded about meeting the great challenges that face our country today - getting on top of our debts and getting our economy to grow.

And that single-mindedness should apply to the subject we're debating in the Commons today: Europe. We need the European Union to contribute to economic growth, not hold it back. That means tackling the crisis in the euro zone that is having a chilling effect on our economy.

It means expanding the single market, so we don't have the ludicrous situation of companies employing teams of lawyers just so they can trade over the nearest border. It means signing free trade deals with the rest of the world. And yes, it means stopping the relentless rise in the EU budget- and we have had real success on that, saving hundreds of millions of pounds that Labour had signed us up for.

There are those who believe we should take an entirely different course. They argue that being in the EU can't help us with growth - and that it's time for a referendum, including an 'in/out' option. I think this is the wrong approach, for three reasons.

First, getting out of Europe would do real damage to our economy. Of course I share people's frustrations about how the EU works. I'm driven as mad by the bureaucracy as anyone else. But we cannot ignore our trade figures - 50 per cent of that trade is with Europe.

I visit countless small businesses whose livelihoods depend on exports to the continent. For their sakes - for all our sakes - it's no use just saying 'Europe's not working for us' and pulling out; single-mindedness means recognising that our membership of the EU gives us a seat at the table at which the rules of that market are made, and we must make those rules work for us.

Second, it's the wrong time to have this debate. We're in the middle of dealing with a crisis in the euro zone - a crisis that if left to escalate would have a major impact on our economy.

If you're putting out the flames on a burning building you need to focus on the job, rather than give up and start a whole new project. You deal with the emergency at hand. That's what we need to do today.

Third, and crucially, there's a danger that by raising the prospect of an in/out referendum, we miss the real opportunity to further our national interest. Many of us have been waiting for a generation for the chance to get the best deal for Britain in Europe.

Now that fundamental questions are being asked about the future of the euro zone, I believe that the opportunity to do that is coming. Put frankly, it would not be in our national interest to act rashly and prematurely, achieve nothing and blow this chance to negotiate a better deal for our country. Those are the reasons why I'm opposed to having a referendum now.

And here's why I have made the decision to whip Conservative MPs to vote with the Government: this issue matters and Parliament matters. The relationship between Britain and Europe isn't some marginal issue. And those of us who believe in the sovereignty of Parliament surely can't argue that some votes don't count.