The other day I compared the saga of Andy Burnham, his ambitions and the forthcoming by-election in Greater Manchester to a long and twisting marble run.

If, and it was a big if, the marble trundled all the way to the bottom, it was possible to imagine Burnham as prime minister, before this year was out.

But, as I said then, it was also possible the marble would fly off the run spectacularly – which is precisely what has now happened.

In an exercise of brute power, which is simultaneously an illustration of how they perceive their own weakness, No 10 has scuppered Burnham’s attempted run from Manchester to Westminster and perhaps on to Downing Street.

Yes, this was a decision taken by a committee of the Labour Party, but allies of Sir Keir Starmer are making it perfectly clear he joined the remote meeting on Sunday morning and he cast a vote to block Andy Burnham.

The relationship between the two men has long been fascinating to observe.

Burnham’s first act in politics was very much as a creature of Westminster: an adviser, an MP for 16 years, a cabinet minister. He has run for the Labour leadership twice before.

Here he is talking to me more than a decade ago about his ambition to be prime minister.

He later reinvented himself – by defining himself against Westminster as the Mayor of Greater Manchester.

But his ambitions beyond the north west of England have long been transparent – and long provoked a roll of the eyes or a raised eyebrow from Sir Keir.

Burnham’s interventions last autumn, around the time of Labour’s annual conference, deeply irritated many within the party. He gave an interview to The New Statesman, which carried the less than cryptic headline “Andy Burnham’s plan for Britain.”

Shortly after came an interview in The Telegraph, headlined “Andy Burnham: MPs want me to challenge Starmer”.

Burnham’s team would point out, rightly, that politicians don’t write the headlines but the wider point stands – his desires were very, very clear.

Just the other day, he set out in The Guardian how he believed his approach to his mayoralty in Greater Manchester could be applied nationally.

Of course, aspiring to lead the country is noble, but it shouldn’t be surprising that the current occupier of that role might have a rather sniffy view of such manoeuvring, particularly when Starmer can argue that it is he who won Labour’s colossal majority not Burnham, whatever people might think of how governing has gone for Labour since.

No 10 has calculated that it would rather weather a short-term storm – the gales of reaction for and against this decision currently gusting across social media – than authorise a circus lasting weeks, then months, with Burnham as a by-election candidate and one question dominating: what’s your plan if you become prime minister?

“I’m afraid no-one is convinced that Andy is coming in to be a team player and the last thing we should do is allow this kind of psychodrama,” one senior party figure tells me, adding: “We can’t allow insecurity and destabilisation to indulge one man’s personal ambition.”

Others are livid, arguing it is absurd and counterproductive to spike the prospects of someone they see as one of the party’s brightest lights.

“You should not block democracy. Keir is running scared and it’s a very bad look,” one senior Labour MP said.

All this means that in the space of just a few months, those loyal to the prime minister have briefed heavily against Health Secretary Wes Streeting, whose ambitions they view with nervousness too – and have now blocked Andy Burnham from returning to Westminster.

They argue that the electorate is sick of political soap opera and they want to get on with governing – against a tricky international and domestic backdrop.

Their critics, within the Labour Party and beyond, say both are acts of a weak prime minister seeking to cripple capable rivals who might, they argue, do a considerably better job than him in No 10.

This will likely be far from the last act this year in the drama of Sir Keir Starmer’s leadership, and how much of a future it has.