Does the United Kingdom really need a new prime minister? In particular, does it need Wes Streeting, Angela Rayner or Ed Miliband, reportedly lining up to replace Sir Keir Starmer?

The answer is surely no, not now and not after whatever the May elections may indicate. A change of government not even two years in office cannot be in the national interest. Yet Britain’s political community appears to be cohering round just such a defenestration. It seems the only way it knows how to hold power to account, giving it the seventh leader inside a decade. Parliamentary democracy is dysfunctional.

First, let us deal with Peter Mandelson. Starmer made him Washington ambassador. The Foreign Office questioned his security clearance but did not impede it. With hindsight, both decisions might have been handled differently. As the Jeffrey Epstein case unfolded, Mandelson’s friendship with the man proved fatal. He was sacked, and now, after further revelations about the vetting process, the head of the Foreign Office, Olly Robbins, has been sacked as well. Matter surely closed.

Costly failures in judgment happen far too often – the Post Office scandal, the Grenfell fire, the overcrowding of A&E corridors and the collapse of NHS dentistry. Billions of pounds are regularly wasted by Britain’s rulers. Many doubtless die because someone somewhere did not say something to someone else. Such matters are seldom debated in parliament and rarely for long. They are boring, complicated and win no headlines.

Mandelson’s appointment led to no squandered billions and no crisis in international relations. The misjudgments involved were largely presentational and anyway Starmer acknowledged this, corrected it and apologised for it. Time and again the crucial issue in politics is what is a proportionate response to any particular matter. The hysteria now enveloping the Mandelson affair shows no such restraint.

Re-enacting the death of Julius Caesar is Westminster’s mode of operation. Since the outcome of any parliamentary debate is usually dictated by the result of the last election, politicians prefer to pick who might be the victim of a poor opinion poll or bad publicity and then hound them out. What finished such leaders as Margaret Thatcher, Tony Blair, Boris Johnson and Liz Truss was not an election result but losing their way amid a Westminster publicity blizzard.

Prime minister’s questions is virtually the only event in the parliamentary calendar that nowadays fills the Commons chamber for an hour or so. At the dispatch box, we witness the downfall of one leader after another: the victim staggers from pillar to post in full view of the nation.

From the moment the Epstein files were released they offered endless material for headlines. According to Private Eye’s cover, Mandelson “let myself down, my party down and my trousers down”. The explosive mix of sex, VIPs and high office, including Donald Trump, was irresistible. Whatever else might be going wrong with Britain, parliament fastened on Starmer. Sacking Mandelson for knowing Epstein was not enough. The craving was for more sackings.

The foreign affairs select committee has been summoning the highest in the land, spinning out their interrogation over days. Forget the Iran war, the state of Britain’s defences, the fate of Nato, or the future of relations with the EU, members wanted to know about the Mandleson vetting process. Meanwhile little else concerned Commons question time. Time and again, MPs leapt to their feet to find a headline for their view of the prime minister’s future.

Leaders of oppositions may rarely say what they would do in office, but they can score points, as the Tory leader Kemi Badenoch has done relentlessly. To call Starmer a liar and demand his resignation over the affair was absurd. It is hard to see this Badenoch displaying the dignity needed for high office.

Westminster is clearly enjoying one of its open seasons. It may well be that it will go on until it does indeed have Starmer is gone. I sense it will then pause and wonder if perhaps that was such a good idea. Perhaps MPs should indeed have spent their time and energy attacking Starmer for the performance of his government, the state of the NHS or homelessness or shoplifting – anything but Mandelson.

Mandelson and Robbins have already paid a bitter price. For the prime minister also to be sacked over this affair would be madness. Getting rid of Starmer at present is out of all proportion to this affair. The crisis again looming over British politics is Westminster playing to its own gallery. It should stop.

• Simon Jenkins is a Guardian columnist