Writing exclusively for City AM, Labour leader Ed Miliband argues that leaving the EU would be a "historic moment of economic self-harm".

We live at a crucial time in Britain’s relationship with the European Union, one which will determine the future of our country for decades to come.

In the past year Nigel Farage, Ukip and a growing number of Conservative MPs who advocate withdrawal from Europe have gained prominence.

At the same time David Cameron has chosen for his own political reasons to flirt with the idea of leaving the EU, and publicly threatening to do so.

I believe both Ukip and the Conservative Party now pose a huge danger to British business and our national interest.

Leaving Europe risks destroying jobs, businesses and future prosperity. And the government’s ritual of playing to the Eurosceptic gallery is dragging us ever closer to the exit door.

Our European allies throw their hands up in despair at the combination of insults, blackmail and detachment that comes from Downing Street. Foreign investors are beginning to regard Britain as a riskier place to do business.

The lesson of the past two years is clear. Using “Brexit” as a threat does not work as a way of getting reform in Europe. It isolates us from the allies we need to achieve the change we want.

It is making it less, not more, likely that we gain support for what is in our national interest: completing the single market, maintaining the integrity of our benefits system, and cutting the costs of the EU budget.

But allies in Europe are growing weary of posturing and threats from Britain. Some are now calling our bluff and telling us we are free to leave. Indeed, when the Foreign Secretary says he wants Britain to “light a fire under the EU”, all he is doing is lighting the fuse on Britain leaving.

I am clear that this would be a historic moment of economic self-harm: a betrayal of millions of people and businesses whose future depends on our EU membership.

Over half of Britain’s trade is with countries in the EU, worth over £200bn a year, and supporting between three and four million jobs.

I know that the vast majority of British businesses, despite the many frustrations and inefficiencies of Europe, want Britain to stay in the EU, and become a leading force in its reform.

We also know that global companies from outside the EU are quite prepared to take their activity elsewhere if we made the catastrophic decision to walk away from EU membership.

Citi, Goldman Sachs & other prominent City firms have warned not only of the damage that Brexit would inflict on our economy, but also of the possibility that international companies would relocate away from the UK “in very short order” to retain access to the European single market.

If I am Prime Minister, I will never risk your businesses, profits and futures by playing political games with our membership of the EU.

But my speech to the CBI will not pretend that we can carry on with business as usual, either in Europe or at home.

The only way we will overcome the forces of despair that drive calls for withdrawal and protectionism is by tackling the deep roots of it in our economy.

Instead of pandering to the false promise of prosperity in isolation from Europe, we have to face up to how to restore shared prosperity inside it. That requires partnership between business and government.

We have to change the way our economy works so that it can once again meet people’s need for good jobs at decent wages, providing security and proper opportunities for the next generation.

To do that we need to address some of the sources of economic weakness: our weak productivity, poor technical skills base, low investment, a recovery too dependent on consumption and an increasing trade deficit.

I passionately believe that making our economy more productive is the flip-side of ensuring we build an economy that works for the broad majority and not just a few.

Achieving this will not be easy or quick, and can only be done through cooperation between government and business: but it is in the interests of us all.

It’s time to come together with our sleeves rolled up to build a recovery which works for the many, and a country that seeks to prosper inside the European Union.