Theresa May has finally admitted we can't immediately close our borders after Brexit – the fantasy is unravelling

Hot on the heels of that imaginary £350m for the NHS, another Brexit lie is crashing in to the white cliffs of Dover

The PM signs the letter invoking Article 50 last week. She is not stupid, and knows that, far from being ‘full up’, Britain’s economy and health service rely on immigration (Reuters)

Outside the lie of £350m a week extra for the NHS, immigration emerged as the best card Brexiteers had to play during the EU referendum. And my, how they exploited it.

Armed with incendiary rhetoric, they cynically played on people’s fears, pledging that if we could just get out of the EU, with its addiction to the free movement of people, we could “take back control of our borders” and everyone would be much happier and richer as a result.

The problem with basing your case on scaremongering, spin and out-and-out nonsense is that eventually it will come back to bite you. Just say the word “Iraq” to Tony Blair.

It’s hard economic reality rather than missing WMDs that is biting Theresa’s May’s Brexit and the fantasy held by some that it would see Government action to "keep 'em out".

How else to explain the PM's hint on her Middle Eastern jaunt that free movement from the EU could last for at least a while after Britain has sailed off into the North Sea?

She is not pledging to keep it. There will instead be “an implementation phase” once an exit deal has been struck, to give business and governments a “period of time” to adjust.

So don’t you worry your sweet little heads, Brexit-backers. Britain will still have greater control over its borders. Oh yes it will!

Quite how is yet to be explained. But let’s park that for now.

May's comments, clearly designed to downplay Brexiteer expectations of a fortress Britain, shouldn’t come as any surprise. I’d imagine that anytime the PM or her more sensible ministers speak to anyone in business they hear the same thing: “Where do you expect us to get our employees from? We need migrants. Could you just pipe down with all that rhetoric about targets? It's killing us!”

The economic problems that will follow any new controls were encapsulated in a report issued last week by KPMG for the British Hospitality Association, which represents Britain’s fourth biggest industry (tourism, pubs, restaurants, hotels) and a reliable foreign exchange earner to boot.

It warned of a 60,000 annual staff shortage facing the sector, based on the assumption that EU citizens who are already here are allowed to stay but new ones aren't allowed in.

And it’s not just BHA members that have genuine cause for concern. There are already indications that problems are building up in the NHS, which relies heavily on EU nurses, for example. They've started to show a marked reluctance to come here. Can you blame them?

“We’ll just train our own up!” bleat the Brexiteers. The trouble is that that takes time, money the Government won’t spend, and people the country doesn’t have.

So they will still have to be imported even after any “transitional arrangements” if Theresa May wants to prevent sucking the economy, and the health service, down a plughole and taking her premiership with it.

The PM regularly played the immigration card while she was Home Secretary, as Tory Home Secretaries, keen to burnish their hardline credentials, are wont to do. She’s in a bigger job now, however, and she knows that while the Conservative Party's poll lead might look all but unassailable as things stand, it won’t remain that way if the economy trips up.

Whatever May is, she’s not stupid.

She will also know, if she's honest with herself, that Britain is not “full up”. As the Thatcherite Institute of Economic affairs made plain in February, EU incomers make up a tiny proportion of the UK population as a whole.

Policy failures, and not immigration, are to blame for the stresses created by a rising population. Waiting too long for an appointment with a GP? It’s because we don’t have enough of them. Struggling to find a council house? It’s because we’ve persistently failed to build enough of them and keep selling off those that we have.

I could go on.

What hard Brexit, driven by a cadre of fundamentalist MPs and tabloid newspapers, offers is not control of “our borders” but the illusion of it. A fantasy that is showing the first signs of unravelling.

There will be more like this in the weeks and months ahead. Anyone want to run a book on the next Brexit promise to crash into the white cliffs of Dover?