Darling and Osborne clash over National Insurance 'jobs threat'

Shadow Chancellor George Osborne demanded internal Treasury papers revealing the impact should made public as Labour insisted the impact was "manageable".

But the Tories are also facing scrutiny over the impact on jobs of their plans to scale back the increase – with experts warning employment would fall by 40,000 under their plans, which have won backing from dozens of major businesses this week.

As the two men clashed in a television interview yesterday, Mr Osborne said: "Why doesn't Alistair publish what we know exists, which is the internal Treasury study on how many jobs will be lost as a result of the National Insurance increase?

"The Chancellor has just repeated on television that job losses from the national insurance increase are manageable. That means there are job losses."

Meanwhile, Mr Darling appeared to acknowledge Labour had been put on the back foot in the first days of campaigning by the Conservative move on National Insurance.

"They might have got their political tactics right for the first day or so but their overall judgment is just plain wrong," said the Chancellor.

Yesterday Tory adviser Sir Peter Gershon, who provided the blueprint for efficiencies to fund Mr Cameron's promise to reverse next year's National Insurance rise, indicated that controls on public sector recruitment would contribute up to one-sixth of the 12bn saving.