Media playback is unsupported on your device Media caption PMQs: David Cameron told to withdraw 'muttering idiot' jibe

Prime Minister David Cameron has been rebuked for unparliamentary language after calling shadow chancellor Ed Balls a "muttering idiot".

He was asked by Speaker John Bercow to withdraw the remark made during a stormy prime minister's questions.

Labour said the PM was "increasingly losing his temper" because he was "losing the economic argument".

Mr Cameron also apologised later to veteran MP Dennis Skinner for "sharp" comments he made to him last month .

It is not the first time Mr Cameron has appeared to lose his cool with Mr Balls, who sits opposite him on the Labour benches, last year calling the shadow chancellor "the most annoying person in modern politics".

'Chillax'

Answering a question on enterprise zones, Mr Cameron hailed the government's economic strategy and said he wanted to find "innovative ways of using our hard-won credibility, which we wouldn't have if we listened to the muttering idiot opposite me".

I can't think of anything Ed would rather have had happen during Prime Minister's Questions Lord Adonis, Labour peer

The remark sparked uproar on both sides of the Commons, with shouts of "Flashman" from the Opposition benches, a reference to a fictional upper class bully used by Labour MPs to attack the prime minister.

Once the Speaker had restored order, he asked the prime minister to "withdraw the word idiot" as it was unparliamentary language.

A smiling Mr Cameron said: "I will replace it with 'the man who left us this enormous deficit and this financial crisis'."

On Twitter, political pundits claimed Mr Balls had upset the prime minister by telling him to "chillax, have another glass of wine" - a reference to a recent book in which Mr Cameron's methods of unwinding from the stresses of his job were revealed.

Mr Balls denied the claim, tweeting: "For the record, I was simply asking the Prime Minister, as he boasted the economy was on track: 'Tell us about the recession'..."

Speaking outside the Commons after the PM's questions session, a Labour source said: "It is deeply un-prime ministerial and a sign of his weakness on the key economic argument."

'Volatile'

Later on, while taking questions on the Nato summit, Mr Cameron also apologised to veteran Labour MP Dennis Skinner, for his "sharp" response to him last month - when he had suggested Mr Skinner should collect his pension and leave Parliament.

He said that he actually believed Mr Skinner was a "tremendous ornament" to Parliament.

Labour peer Lord Adonis said Mr Balls would have been delighted to have provoked another reaction from the prime minister.

"Almost every week the prime minister turns himself into the personal publicity machine for Ed Balls," the former transport secretary told BBC Radio 4's The World at One.

"I can't think of anything Ed would rather have had happen during Prime Minister's Questions than to be called an idiot by David Cameron. He will be dining out on this for weeks to come and it will do his standing huge powers of good."

But Lord Lamont, who was Mr Cameron's boss when he was chancellor in the early 1990s, defended the prime minister, saying: "He can be quite volatile... I think that makes him more engaging."