Mr Clarke's three years at the helm is, in fact, one year less than Dalton Philips has had so far at Morrison, or his predecessor Marc Bolland at the helm of M&S. Neither has made any great strides forward, and Morrison appears to be in a state of chaos; its last reported like-for-like sale figures in May were the worst I can remember seeing from any grocer, a drop of 7.1 per cent. Luckily I am not really a betting man because after that performance I thought Mr Philips' position was untenable.
As it happens, in Morrison's case, it is the chairman Sir Ian Gibson who will be leaving, announcing plans to step down less than a month after the grizzly figures were revealed. Cause and effect? Who knows, but it looks very much to me like Sir Ian took the easy way out - a much harder task would surely have been to admit the chief you've hired isn't up to the task.
That's not to say that in Tesco's case the chairman has acted alone; it has been suggested that shareholder pressure has paid a large part in Mr Clarke's removal. Perhaps that pressure was necessary, because the decision to dump a man who had served his company for nigh on 40 years cannot have been an easy one.
That also raises an interesting point about succession planning, and whether firms should elevate born and bred insiders over external hires to the top jobs. Analysis suggests that insider appointments often do better than external hires. But experience is more mixed. An insider should know his company and its culture intimately, and be able to hit the ground running. Or it can lead to a perpetuation of outdated ideas and risk alienating other able insiders, who leave - the so called 'brain drain' that Mr Clarke suffered upon becoming chief executive.
The external hire can cause similar problems, the predictable departure of finance director and steady hand Richard Pennycook from Morrison a case in point. And although there is a lot to be said for the new ideas an external hire can bring, it can also take some time for them to understand the business they've inherited. Dalton Philips' biggest mistake has arguably been his failure to move quickly enough to embrace the triple challenge of online, convenience and hard discounters.
Internal or external, what ultimately matters is having the right person at the helm - and there are many managers of FTSE companies worth backing. But even the best of them aren't miracle workers.
