David Miliband accused of mounting a campaign to 'destabilise' Gordon Brown

A Whitehall row over spin was in danger of escalating after the Foreign Secretary was accused of reviving his ambitions to challenge for the leadership.

Days of tetchy exchanges between Downing Street and the Foreign Office culminated in claims that Mr Miliband has been behaving "disgracefully".

The Foreign Secretary tried to clear the air yesterday, insisting he was 'proud' to be working under Mr Brown.

But his enemies accused him of engineering a dispute to put distance between himself and the Prime Minister at a time when polls show public confidence in Mr Brown is falling.

They said he was trying to burnish his leadership credentials barely six months after standing aside to allow

Mr Brown a clear run at the Labour crown.

The squabble started last week as a minor dispute over a speech on Europe by the Foreign Secretary.

Mr Miliband was said to be angry after Downing Street asked him to tone down elements of his keynote address on European defence policy.

But the Observer newspaper reported Mr Miliband's "friends" - Westminster code for the Foreign Secretary himself - said he was also "unhappy" as Foreign Secretary and felt excluded from the Number 10 inner circle, which is dominated by Schools Secretary Ed Balls.

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Mr Balls is being promoted by Downing Street as a key Cabinet player, and is widely seen as Mr Miliband's main rival in the event of a leadership contest.

The former Treasury adviser is talked of as a future chancellor and is said to be the Prime Minister's favourite to succeed him when the time comes.

Downing Street sources played down the dispute yesterday as nothing more than a Foreign Office briefing operation that went awry.

The story emerged after passages of Mr Miliband's speech e-mailed to journalists were different to the final version of the speech he delivered in Bruges.

Mr Miliband tried to undo the damage in a BBC interview in which he praised Mr Brown and said it was "absolutely wrong" to suggest there had been a breach between them.

"I'm proud to be serving under Gordon Brown's leadership in government. He and I are working together very closely," he added.

Mr Brown's allies also point out that the Prime Minister has consulted on foreign policy with Mr Miliband far more extensively than Tony Blair allowed when he was in power.

But, commenting on Mr Miliband, a Labour source told the Daily Mail: "There's a feeling around that he's trying to rerun his leadership campaign and, fairly disgracefully, destabilise Gordon Brown.

"His friends believe he'll be in a stronger position if he distances himself from Mr Brown when he's in trouble.

"David should remember that he could have stood against Gordon in the spring. He had his chance. And he didn't take it because he knew he would have been murdered politically."

The tension comes as David Cameron is grabbing headlines with policy initiatives such as a literacy and schools discipline drive and Downing Street fears its message on policy is being drowned out by internal disputes.

A YouGov poll yesterday suggested fears about the state of the economy and the handling of the Northern Rock crisis have also sharply dented Mr Brown's standing with voters.

Where 59 per cent believed he was doing a good job as Prime Minister last month, just 33 per cent approve of his performance now.

The poll also confirms the Tory lead over Labour, 41 per cent to 35 per cent.

Mr Brown will try to draw attention away from internal squabbles today with a major speech on the environment, his first as Premier.

In the wake of the latest warnings on the scale of climate change from the UN, Mr Brown will offer to raise Britain's target for cutting greenhouse gas emissions by 60 per cent by 2050.