I'll know if Brexit has worked.

So, the deed is done and the letter has been delivered - the Brexit process has begun.

In an excellent and thought provoking piece in The Guardian today, Rafael Behr argues the case that there is no going back now. And more to the point, no matter how badly it goes, the Brexiteers will always be able to argue the case that it's only because its not a tough enough Brexit, and if only it was done properly, all will/would have been well.

The problem as he sees it, it that there's no alternative history to compare and contrast. As Rafael puts it...

"Pro-Europeans will struggle to disprove those arguments because there will be no demonstrable counterfactual. The claim that Britain would have been better off on a different path will be no more effective than the prediction in last year’s referendum that Brexit would hurt. No one who ignored that warning wants to be assailed with a smug chorus of “we told you so”. "

And its on this point that I disagree with Rafael. Because I fear there is a counterfactual.

While I think on balance, Britain will be economically worse off out of the EU rather than in, this was never my overarching reason for voting 'in'. Indeed, I suspect there's a lot of guesswork on both sides around the economic ups and downs of Brexit.

No my reason is different - and one where a strong counterfactual does exist.

I've been fortunate enough to see some wonderful Statesman and women speak over the years- I saw Reagan speak on Capitol Hill, I heard Helmut Kohl speak when I was a student - but the greatest political speech I ever heard 'in the flesh' was given in a meeting room in Portcullis House about 15 years ago - by Michael Heseltine.

He spoke, without notes for maybe 20 minutes, about peace in Europe. He was informed, authoritative, mesmerising, running over maybe 100 years of European history and arguing the case for why it was the EU that had delivered, for the first time, long term peace in Europe.

I have never forgotten it.

I am also of an age that I grew up at a time - the 1970s - when the Second World War may have seemed to us as children as ancient history, but we played football around the air raid shelters in the park, and the railings of the houses in our streets were just stumps in the wall, the metal having been removed (we were told) to make munitions. This makes peace seem a little more fragile perhaps than many people remember.

Similarly war in Europe is not a remote, ludicrous proposition. What we often refer to quite glibly as 'the troubles' is anything but a distance memory, and we have had war in Europe in the recent past, and indeed in the Ukraine right now. It's not coincidence that no EU country has been involved in this.

So my counterfactual for Brexit is this; peace in Western Europe for the next 44 years.

Anything less and Brexit is a failure.