Mr Miliband finally stepped out of the shadow of his older brother, Foreign Secretary David Miliband, with a lucid performance in front of trade unionists who have already marked him up as a possible future Labour leader.

David Miliband, once seen as a potential challenger, is now seen as having blown his chances after twice failing to find the courage to move against Gordon Brown. With another leadership challenge against the Prime Minister unlikely, the horizon is now being scanned for the next leader.

Harriet Harman, the Deputy Leader, was at a private TUC dinner in Liverpool on Tuesday evening burnishing her credentials with union leaders, but the 39-year-old Mr Miliband stole the limelight from her.

Like his namesake and potential rival, Schools Minister Ed Balls, Mr Miliband is a Brownite but he is far enough removed from the leadership to avoid being identified with electoral failure.

It is hard to evoke the class war when talking about loft insulation but Mr Miliband managed to get applause on the issue in what was the best political speech the Liverpool conference heard yesterday.

He adopted the David Cameron style of pacing the stage in shirt sleeves delivering without notes a speech that had nonetheless been thoroughly memorised beforehand.

Half way through it looked as if his address would be hi-jacked by the sacked Vestas wind farm workers from the Isle of Wight, who received a standing ovation when he acknowledged their presence in the hall and their problems.

With the audience turning their back on him, the minister recovered well from the situation. Why, he asked, did Vestas not have enough orders for wind farms in the UK? “Because 60% of wind farm applications are turned down by Tory councils,” he said.

He continued on his theme of how climate change presented a great opportunity for jobs and to the delight of trade unions called for a trinity of clean coal, nuclear and renewables.

Derek Simpson, the joint general secretary of Unite, the largest Labour union backer, has already tagged Mr Miliband as a potential leader and the Doncaster North MP played to the gallery with a blistering attack on the Conservatives that had been missing from Gordon Brown’s speech the previous day.

“It’s not green to put a wind farm on your roof when time after time wind farm applications are turned down by Tory councils,” said Mr Miliband tearing into David Cameron.

“It’s not green to visit the Arctic circle, but when you’re in Europe to pal around the fringes with climate change deniers. It’s not green to ride your bike to the House of Commons to vote against investment in green industries.”

It went down well, especially when he compared the Tory idea of public services to the Ryanair model – lots of queuing with the many making do on the bare minimum, while the few paying extra for a better service.

“It works for an airline but it’s no way to run a care home or a hospital,” said Mr Miliband.

Since becoming Energy Climate Change Minister Mr Miliband has made decisions he did not necessarily have to take if he wanted a quieter life. He brought forward the 2050 targets for carbon reduction and included air travel in the equation, for example, proving he is capable of making bold decisions.

As this December’s UN Climate Conference in Copenhagen approaches, his public profile will increase and so too will Ed Miliband’s chances of one day becoming Labour leader.