“I thought that when he called the referendum, probably we were going to have a sensible, if not an intellectual, debate about the pros and cons of the EU.

“And I do believe that if they had set off to set out what they saw of the advantages and the disadvantages on the other side, and it had been a balanced debate, then they would quite easily have come out with a Remain conclusion.”

However, he warned: “They launched very early into this attack, this description of all the horrors that would happen if we exit. I just listed to this and thought, ‘this is complete nonsense’.”

Sir John said that he was “quite upset” by Mr Osborne’s decision to release a Treasury document warning that a Brexit will leave British families £4,300 a year worse off.

“I thought to myself, ‘is this a joke? Is the Chancellor really suggesting that anyone can predict what the world will be like in 2030? How is this possible?” he said.