What is really going on in politics? Get our daily email briefing straight to your inbox Sign up Thank you for subscribing We have more newsletters Show me See our privacy notice Invalid Email

Theresa May had a prop at PMQs today - which she used to attack Jeremy Corbyn over Labour's economic policy.

She claimed the book, Economics For The Many , edited by Shadow Chancellor John McDonnell, declared Labour's costed manifesto "doesn't add up".

But within minutes, it became clear it was Mrs May's claim that didn't add up.

The Prime Minister went on to claim the book stated that the numbers not adding up was "entirely appropriate" and "a welcome feature."

Again, that's not quite how the book puts it.

Here's what the book really says, and why the Prime Minister using it to claim Labour would "wreck the economy" was being being economical with the facts.

What is the book?

The book chapter Mrs May referred to is by Simon Wren Lewis , an economist and member of Labour’s Economic Advisory Committee.

What does it actually say?

(Image: PA)

The chapter in question is about Labour’s Fiscal Credibility Rule (FCR) - which sounds complicated, but it isn’t really.

In short, it promises to ensure

The Government is spending less than it takes in in tax within five years

Government debt is falling within five years

Labour will only borrow for investment and infrastructure, not for day-to-day spending

But does he say Labour’s sums didn’t add up?

No. He said other people said they didn’t add up. And he said that it didn’t matter.

What the chapter actually says about the Labour manifesto is not that it ‘doesn’t add up’, but that it notes that the Institute for Fiscal Studies claimed it ‘doesn’t add up’ - which is a very different thing.

And the IFS didn’t really say that . It said that it was “hard to say” whether Labour’s pledge to reduce debt was compatible with their promises of a wave of nationalisations of water and energy.

Their argument was essentially that because Labour would transform the economy so radically, it would be impossible to say whether their manifesto costings would be accurate.

They said: “This manifesto cannot be summed up in mere numbers.”

OK, let’s dive into the details

Meanwhile, back in the book, Professor Wren-Lewis goes on to say that because interest rates would most likely have remained historically low by the time Labour won power, their spending commitments would help the economy recover.

He wrote: “Let us suppose the IFS was correct, and the tax measures outlined by Labour were insufficient to match their proposed spending increases.

“There were two possibilities. First, and the most likely given the Brexit slowdown, interest rates would have remained at their lower bound. In that case the FCR would have said that the resulting fiscal stimulus was entirely appropriate and welcome.

“The fact that the numbers ‘did not add up’ would have been a welcome feature of Labour’s manifesto, because it would add to the fiscal stimulus.”

His second suggestion was that if the economy suddenly recovered, the deficit would fall as a result and Labour may well have been able to fund all the spending increases and stick to their rules.

He added: “As a result, the fact that the numbers might not have added up was largely irrelevant.”

Mrs May selectively quoted that section to make it look like Professor Wren-Lewis was criticising Labour’s strategy, but he wasn’t.