It is no secret, but all is not well between the prime minister and his chancellor.

This time last week Rishi Sunak appeared to be the one who was in trouble following revelations about his wife’s tax affairs. By this week the balance had tipped. Boris Johnson is now the more vulnerable of the two.

Whatever the particulars, however, it is never a good idea for a chancellor to fall out with his prime minister. For one thing, it doesn’t make for stable government and for another it tends to rebound, often to the disadvantage of both parties.

The rift between Gordon Brown and Tony Blair is the stuff of legend. A fault line that ran through the Blair government’s entire period in office. The breakdown in relations between Margaret Thatcher and her Chancellor, Nigel Lawson, brought about Lawson’s demise – and was a major factor in hers.

In Labour’s case the seeds were sown from the outset when Blair leap-frogged Brown in the race to succeed John Smith. It was also, at least insofar as Brown was concerned, deeply personal. In the early years news of the rift was suppressed, principally due to the media management skills of Alastair Campbell. As Campbell once remarked to me, “For years I was required to defend a lie. That all was well at the heart of new Labour when it wasn’t.”

Looking back it was remarkable that the lid was kept on for so long. Brown in effect set up a rival court in the Treasury. Damaging leaks and hostile briefings seemed to come from someone in Brown’s inner circle. Blair used to profess himself mystified. “Where is this stuff coming from?” he would ask at meetings of his advisers and one of them would silently point in the direction of the Treasury.

In fairness to both men, they understood just how damaging the stories of a breakdown in relations between the two most powerful members of the government could be and always drew back from the brink.

More than once Brown appeared to endorse rebellions by his back bench supporters in parliament only to retreat at the last moment. When Blair was in trouble over Iraq, Brown never sought to exploit the issue. For his part Blair several times contemplated removing Brown from the Treasury, but always drew back for fear that the fall-out would prove ruinous.

In the end, despite everything, they just about got away with it. In June 2007, after ten years in office, Blair departed more or less on his own terms and there was an orderly transfer of power. Along the way, however, it was white knuckle ride.

Rishi Sunak is not in so strong a position as Brown. A relative newcomer to politics his rise has been meteoric, but easy come, easy go.

True, his deft handling of the economy during the Covid lockdown won him friends in all quarters, but the acclaim he received did not necessarily endear him to his next door neighbour. His apparently lukewarm support for the prime minister during his troubles over ‘party gate’ was widely noticed and talked about.

For the time being they will stand or fall together. In the longer run, however, the shine has come off ‘Dishi’ Rishi. His Non Dom wife and the news that he was in possession of a US green card until recently make it look as though the golden couple have just stopped over to govern us for a few years while en route between India and California.

Moral of story: thou shalt not covet thy neighbour’s job.

At least not too conspicuously.

Chris Mullin is a former Labour minister and the author of three volumes diaries charting the rise and fall of New Labour