EU referendum pledge: A huge moment in British politics

Most heavily hyped and much trailed speeches end up being a crashing anti-climax, but it would be hard to argue this conclusion to David Cameron's address today for the simple reason that for the first time in a generation the possibility of the UK leaving the European Union is on the mainstream political agenda.

The Prime Minister's argument was clear enough; most of our European neighbours are on a train to ever closer union that we never voted to get on and now definitively want to get off.

Indeed, what he was really saying was that we want to go back a few miles to the station marked 'single market' and then park the train there for the foreseeable future.

As you will have read by now, he promised an in and out referendum in the first half of the next parliament with a draft bill to be agreed before the next election.

Many of his eurosceptics are ecstatic, as well they might be; he gave them pretty much everything they wanted.

David Cameron's speech will have appealed to many eurosceptics Credit: Stefan Rousseau/PA Wire

In answer to a shrewd question from the Evening Standard's Joe Murphy, he even seemed to make it a coalition busting issue in 2015.

If I am Prime Minister, he said, this referendum will happen.

Or in other words; he is making Europe the non-negotiable issue of the next parliament before we have even got close to that point. One does wonder if he will regret that.

In terms of intellectual clarity, the speech only really had one big weakness, which was that he was pretty vague about exactly what powers he wants back from the EU.

He will need to flesh these out as the months progress, but no one can say this was anything but a huge moment in British politics.