26/11/2017 12:06 GMT | Updated 27/11/2017 11:46 GMT

Watch As John McDonnell Uses Robert Peston's Own Book To Justify Labour's Spending Plans

"There was a very good book published a month ago..."

John McDonnell turned the tables on ITV’s Political Editor today by using the journalist’s recently published book to justify Labour’s spending plans.

The Shadow Chancellor quoted from Robert Peston’s “WTF” as he explained why Labour would borrow an additional £250billion to invest in the UK – despite the country already being in £1.8trillion of debt.

Peston was heard to mutter “Yeah I know what’s going to happen now” as McDonnell began referencing is latest book, leading the journalist to chuckle to himself as he heard his own arguments thrown back at him.

The Shadow Chancellor said: “There was a very good book published a month ago which actually said, the author said, we’ve got to stop being frightened off, by the myths around public investment and we have to use public investment to grow our economy, and I think you were right in that book.”

Peston pointed out his book also argued for “the importance of politicians telling the truth to the public” as he quizzed the Shadow Chancellor on how much it would cost to borrow the extra money.

When asked if he agreed with the Institute of Fiscal Studies analysis it would cost an additional £2billion a year, McDonnell replied: “No, I can’t predict it.”

He explained he was not able to predict what the cost of borrowing would be by the time Labour got into Government.

McDonnell also used the interview to apologise for his behaviour during a post-Budget interview with the BBC earlier in the week, where he accused presenter Mishal Husain of “trite journalism” when asked how much Labour’s spending plans would cost.

He said at the time: “The type of journalism where you go into an interview and they ask you a question on a particular figure is a trite form of journalism - it’s why we have iPads and advisors.”

Speaking on Sunday, he said: “I’m sorry if people thought I was arrogant, but what I was trying to do was not get dragged down into an argument which prevents people realising we do actually need to invest.”

The Tories hit back at Labour’s economic plan, and Chief Secretary to the Treasury Liz Truss, said: “Labour can’t say when they’d eliminate the deficit because with their eye-watering borrowing binge, they never would.

“And their Shadow Chancellor - the man who doesn’t do numbers - again refused to come clean on how much that borrowing would cost taxpayers. 

“Labour would saddle future generations with a mountain of debt, meaning higher taxes and fewer jobs. Once again, ordinary working people would pay the price.”