The best description of our new politics is that the truth is whatever leaders like Donald Trump and Vladimir Putin want it to be. Stuck in old fashioned mores and habits, mainstream journalists and analysts hesitate to accuse US presidents and UK prime ministers of lying.

But post-truthism demands a robust and clear response: when these people lie they need to be called out for what they are: liars

When Theresa May says that the Leave campaign was crystal clear about exiting the single market she is lying.

Boris Johnson, Nigel Farage, Daniel Hannan and many other prominent Leavers can all be looked up on YouTube declaring their affection for the single market and assuring us that free trade with the EU, usually via a Norway/Swiss-style associate membership, would not be threatened by Brexit.

“Orwellian” is an overused term, but seems particularly apposite right now. May spent most of her time at the Home Office failing to curb immigration despite being single-mindedly devoted to that objective.

She can now resume the fight, but this time with more chance of success.

For her and the ideologues in the UK government this is the order of priorities: curb immigration and accept the economic costs but don’t admit this – lie some more.

Claim that the economic costs associated with hard Brexit are the exact opposite of what we know them to be.

Damage growth

May tries to pin low growth, low wages and the crisis in NHS funding on immigration. Even Orwell couldn’t have dreamt that one up.

The truth, as opposed to the lies, is that lower immigration will damage growth and yield lower taxes for the NHS and other welfare-spending programmes.

Remember the Nissan deal? In the immediate aftermath of the referendum the Japanese car-maker sought reassurances on British access to EU markets.

It received a letter of comfort from the government, the contents of which have not been revealed.

I’m willing to bet Nissan was lied to – unless it swallowed a promise that Britain would have unfettered free trade despite leaving the single market and probably the customs union.

Believing in six impossible things before breakfast is not a trait usually associated with successful multinationals. Nissan executives must be rereading that letter with astonishment and a lot of buyer’s remorse.

The specific claim – lie – on the economic benefits of leaving the single market is that the benefits of newly-negotiated free-trade agreements with non-EU countries will outweigh the costs of loss of access to EU markets.

The respected National Institute of Economic and Social Research has said that this is nowhere near being close to the truth.

You cannot ignore geography and gravity: loss of free trade with Europe will have costs vastly in excess of the gains from trade with places further afield.

Specifically, UK trade could get a 2.2 per cent boost from non-EU free-trade arrangements but will suffer a 22 per cent hit from loss of single market access.

Unanswered questions

One of the big unanswered questions focuses the on the jobs that migrants do. They are many and varied, often highly skilled.

But there are plenty in the caring and hospitality sectors that are not typically skilled. And they are increasingly done by migrants.

Who in their wildest imagination imagines that British workers are suddenly going to do all those jobs once the immigrants stop coming?

It’s already a country with full employment and, unlike the US, an all-time high employment ratio (the proportion of the population in jobs).

Without the migrants there are going to be a lot of old and sick people without proper care and tourists complaining about plummeting standards in hotels, pubs and restaurants.

Arguably – and ironically – Europe’s single market can be said to be Margaret Thatcher’s greatest achievement.

It was driven, behind the scenes, by Britain in an explicit response to UK corporate lobbying for greater access to Europe’s markets.

Powell’s speeches

More generally, it should never be forgotten that the UK joined the (then) common market in 1973 because it was correctly viewed as the only way to address Britain’s ongoing economic decline. And it worked. And now they want to leave.

But this is not about economics. The roots of the Leave campaign can be found in Enoch Powell’s speeches in the 1960s and 1970s.

He also claimed that Britain would be better looking out to a free-trading world rather than an inward-looking Europe. Of course, then as now, it was more about thinly-veiled racism than economics.

May’s 12-point strategy will not survive its first contact with the enemy. The plan’s lies, contradictions and inconsistencies will be obvious to the EU-27.

And they now know that they are the enemy: the threats from May and her chancellor to turn the UK into an offshore low-wage, deregulated tax haven have seen to that.