The wrong man has resigned in the scandal over Barclays and Libor. Knowledge of an attempt to manipulate rates would have been way below the pay grade of the bank's departing chairman, Marcus Agius, who steered the bank through the 2008 financial crisis without asking for a taxpayers' bailout. The chief executive, Bob Diamond, by contrast, was directly responsible for Barclays Capital at the time.

Senior management there was aware of the deception, which was designed to calm market jitters about the bank's stability, the Financial Services Authority investigation has found. When Mr Diamond, who has a reputation as a very hands-on manager, appears before the Treasury Select Committee tomorrow, MPs must confront him with the bald alternative that if he did not know about the rate-rigging, he is incompetent – and if he did know, he was complicit.

They should not be deceived by the resignation of Mr Agius, who had been planning to go next year after the emergence of vocal opposition at the last AGM to his proposal to increase Mr Diamond's annual pay package to £17.7m. Mr Agius, an old-style former investment banker, appears to have been too weak to manage the brash Mr Diamond.

The Barclays board remains unanimous that the American should stay because he is a top performer in an industry where making money seems to be the only yardstick. Finding a new chairman is easy; replacing Mr Diamond would be far harder. But this is the wrong judgement. He may be good at banking, but he misjudges its wider implications. Perhaps that didn't matter before; it does now.

Let us not forget that Mr Diamond is the man who gave a hostage to fortune by saying last year that the time for bankers to show remorse was over, when he knew the FSA investigation into Libor fixing was under way. While adept at the technicalities of banking, he would seem to have little grip on the reputational implications of such actions.

If Barclays is to restore its good name, it needs someone with a better grasp of both the politics and the ethics.