There must be a lot running through his noggin. He must be stunned at the pace of his rise to power. He stood for the Labour leadership twice and lost both times after two long and bruising campaigns. Now he’s about to be crowned both Labour leader and Prime Minister of Great Britain. Power has fallen at his feet, simply by winning a local by-election.

Burnham’s arrival at Euston station yesterday was treated like an epic moment in history. Right up there with Vladimir Lenin’s train pulling into St Petersburg in 1917, at the start of the Russian revolution. Or the Ayatollah Khomeini landing at Tehran airport in 1979, days before the Shah fled Iran. Let’s hope the outcome isn’t quite as disastrous. I don’t think Burnham is a Bolshevik, and I’m pretty sure he has no plans to impose theocratic rule, but there are worrying signs that he’s not the saviour many think.

Burnham has a string of huge decisions to make. Some look done and dusted. Rachel Reeves will be removed as chancellor. She watched yesterday’s coronation ashen-faced, and understandably so. We may miss her more than we think, because fresh reports suggest Burnham is about to do the unthinkable and replace her with energy secretary Ed Miliband.

Right now, Red Ed is pushing his claim and so are a string of figures within Burnham’s entourage. Miliband helped secure Burnham’s path to power by stabbing his previous boss Sir Keir Starmer in the back, front and sides. And he’s desperate to be made chancellor. It’s his dream job. He previously showed the country he wasn’t cut out to be Labour leader, but entering Number 11 is the next best thing. From there, he can direct economic policy and the fate of Burnham’s government.

Naturally, that would be a disaster for the country. Miliband’s madcap net zero charge will cost us tens of billions, or even trillions, as he pursues impossible targets to impossible timetables. All to satisfy his own ideological zeal. His decision to crush our domestic North Sea oil and gas industry is rank madness. He’s hammered businesses and households, while accelerating the deindustrialisation of Britain. In fact, he seems to be following Lenin’s mantra of “the worse, the better”.

If Miliband is allowed to apply the same thinking to the entire economy, it would be a nightmare. Financial markets are terrified at the thought. Gilt yields would rocket, costing us billions more in extra interest. Even more wealthy taxpayers will flee, while the rest of us will face the autumn Budget from hell. Even the unions are worried about Miliband’s trail of destruction. Sharon Graham, general secretary of Unite, has urged Burnham to rule Miliband out of the running. Publicly.

This is Burnham’s last chance to block him. Once Miliband is installed, he’ll be unstoppable and immovable. He steamrollered both Starmer and Reeves, when they tried to stand in his way. He’ll steamroller nice guy Burnham too, especially once Andy’s early gloss has worn off.

The relationship between the PM and chancellor is the most important in government. When they’re at odds, it ends in disaster. When Margaret Thatcher fell out with her chancellor Nigel Lawson, that was the beginning of the end for her. New Labour chancellor Gordon Brown devoted his energies to forcing out Tony Blair, only to prove a disaster when he finally muscled his way into power.

Miliband would be a liability because he’s not a team player. He’ll go his own way, and won’t stop, regardless of the opposition he encounters or the damage he does. Yet Miliband is still the frontrunner. His supporters and left-wing press are pushing him relentlessly. Burnham’s mistake? He’s listening to them.

There’s still a slim chance that Burnham could promote the more moderate Wes Streeting, or veteran Yvette Cooper. But today, Miliband is the favourite. If Burnham picks him, he’ll regret it. It could sink his chances of reviving the UK economy, right from the start. His first error could be the biggest of all, and a disaster for the UK. Maybe yesterday’s train ride will go in down in history after all.