Lord Mandelson did something unusual recently. He praised Ed Miliband, calling him “the man with a plan.” The point Mandelson was making is that while some in the new cabinet have struggled to adjust to being in government, at least Miliband has been in office before and is on a mission. He knows what he wants to do – to decarbonise Britain’s energy system and in doing so supposedly save the planet – and he and his team of advisors have cracked on at a ferocious pace since Labour took power in July.

The reason Mandelson’s praise was so striking is that he was a critic when Ed Miliband was the ill-fated leader of the Labour party between 2010 and 2015. When some of us were saying in that period – me included – that the highly driven Miliband should not be underestimated, Mandelson as an architect of New Labour thought leftwing Ed was being overestimated. In the end, Mandelson was right and Miliband was defeated by David Cameron in the 2015 general election.

What has always struck me about Miliband since I first met him more than twenty years ago is his determination and enthusiasm, that sometimes tips over into fanaticism in pursuit of what he regards as a virtuous goal. Having seen government from the inside, as a key adviser to Gordon Brown in the Treasury after 1997, and then in cabinet before 2010, he clearly understands that he has no time to waste. Cabinet ministers – even those friendly with the Prime Minister – are dispensable, so if you want to get something done you need to start early and have a plan.