Ed Balls faced embarrassment yesterday after being accused of shouting "so what?" as MPs heard Britons were paying more tax than ever before.

The Children's Secretary, Gordon Brown's closest Cabinet ally who is widely tipped as a future Chancellor, was rounded on by Conservative leader David Cameron as he heckled his Budget response.

His apparent jibe came as it emerged he and his wife, Yvette Cooper, who is Alistair Darling's number two at the Treasury, earn almost £600,000 in salaries and expenses.

He interrupted just after the Conservative leader had warned Britain was woefully ill-prepared for the troubled economic times ahead and now had the highest tax burden in our history.

Hearing Mr Balls interject, Mr Cameron replied "'So what', says the minister for children. I know he wants to be Chancellor so badly it hurts.

"I have to tell him - another Budget like the one we have just heard and he won't have to wait very long."

Later, as Mr Balls continued to shout excitably, the Tory leader added: "I know he is the minister for children, but he doesn't have to behave like one."

The Children's Secretary has denied saying "so what" and his aides claim Hansard, the official record of Parliamentary debate, had agreed not to include the remark.

"He said 'so weak' as a general criticism of David Cameron's response. It's tradition to heckle the leader of the Opposition during his Budget response," one claimed.

But Tory work and pensions spokesman Chris Grayling said: "This just shows how out of touch ministers have become.

"People up and down the country are facing big rises in the cost of living, but the Government just doesn't seem to understand that they can't afford more tax rises."

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