Sketch: What's four grand when you don't earn £45,000? Don't ask me I'm a millionaire

Arron Banks, founder of the official unofficial Leave campaign, faces the Treasury Select Committee and cannot stop laughing at his own jokes

Leave.EU and founder and Ukip donor Arron Banks is questioned by the Treasury Select Committee (Parliament TV)

Finally, some important context on why the projected £4,300 cost per household of leaving the European Union would be “a bargain”. The chap who said it, Ukip bankroller Arron Banks, now thinks the average UK salary is £45,000.

With allowance for rounding error, he was out by about 100 per cent. Helen Goodman of the Treasury Select Committee told him it was in fact £25,630. But before you are too quick to judge, bear in mind this is a man who has a spare million quid to give to Ukip.

He’d been called to give evidence in his new role as founder of Leave.EU, the now unofficial Out campaign. And he’d brought along his co-founder, semi-suave businessman Richard Tice. One time Gove acolyte and Whitehall wind-up merchant Dominic Cummings had done the same last week. He’s running the official Out campaign, Vote Leave, and the two aren’t speaking. These are, you will already have noticed, the indispensable facts of which you must familiarise yourself before you gravely discharge your democratic duty in less than two months’ time.

The session began with a brief run-down of the insults Mr Banks, a 50-year-old Bristolian businessman, has in recent weeks aimed at his enemy – that being not the EU but Vote Leave. “These people are jokes,” the permanently Sahara-dry committee chair Andrew Tyrie reported he had said. “Dominic Cummings is a liability.” The other head of Vote Leave, Matthew Elliott, apparently “wants to be Lord Elliot of Loserville”.

Banks’s shoulders erupted. The honour of having your own jokes – if that’s what they were – read back to you in official parliamentary proceedings is a rare one.

With a relatively short time to go until the referendum, there are those who hope that the various Out campaigns’ energies will be devoted to campaigning for Out, rather than against each other, but that time has not come yet.

“Vote Leave is a Tory campaign with a few bits added on,” Banks said, having finally suppressed the smirks. “It does not represent the wider Eurosceptic movement.” And that’s what’s important.

Most of the MPs on the Treasury Select Committee are former economists, and nowhere is the old joke about putting four economists in a room and getting five opinions in more fulsome evidence.

The interrogation from Helen Goodman moved quickly between interest rates in Switzerland, Japan and the EU and was only brought to an end when Mr Banks segued on to the unlikely territory of his son’s piano lessons. “My son’s piano teacher told me she didn’t like Obama coming here and telling us what to do,” he said.

“I’m not asking you about your child’s piano lessons,” Ms Goodman replied.

Besides, what are Barack Obama’s opinions worth when, as Tice suddenly intervened, “Ted Cruz has said in the past 24 hours that he’ll put Britain at the front of the line for a trade deal not the back of the queue”.

I’m no economist, but I think I remember that to get the probability of multiple events, you multiply the odds. It may indeed come to pass that Britain votes to Leave and Ted Cruz wins the Republican nomination and then beats Hillary Clinton to the White House, but some rudimentary calculator work on a bookies’ website indicates that is roughly as likely as Leicester City losing the Premier League title and Jamie Vardy being named the next President of the European Commission.

It didn’t all go Ms Goodman’s way. A few minutes later she was reading out Mr Tice’s CV, and telling him he had “been CEO of Valley National Finance.”

“No I haven’t,” he told her. “I’ve never heard of it.”

“But this is the CV you submitted to this committee,” she replied.

“No it isn’t,” he said.

It turned out it wasn’t. “It might be from Bloomberg,” someone else said.

Next up was, “a company called Tice Farms.”

“There is no such entity,” he told her.

Before it could descend completely to farce, Mr Banks generously intervened to point out the whole thing was a waste of time. They’d been summoned to discuss the “financial implications of Brexit” – that, at any rate, is the title of the committee’s forthcoming report. But this, it transpires, is a side issue that in fact is of no interest to the chief businessman backing Brexit.

“The right to make our own laws is paramount above all else,” Banks said. “I don’t think when people were storming up the beaches of Normandy they were saying ‘this is going to cost us two thousand quid’. It’s an extreme example, but I equate the European Union with that.”

When you put it like that, what’s £4,300? Or £45,000? Or £25,000? Or a million? Or whatever other numbers are doing the rounds? Except, it’s nothing like that, is it?