The timing of UBS’s $2bn loss at the hands of a single trader could not have been better for supporters of profound banking reforms such as those proposed by the UK’s Vickers review. It could also not have come at a worse time for European banks, again in the grip of uncertainty. We must hope that the former outweighs the latter.

Whatever else Kweku Adoboli, the UBS trader arrested in connection with the loss, has done, he has tilted the politics of banking regulation to the reformers’ advantage. The revelations come on the third anniversary of the Lehman Brothers bankruptcy. Everywhere, those who feel that bankers got away with reckless endangerment must be thinking: “there they go again”.

That is in part true, but only in part. $2bn is an enormous sum of money and losing it is a big scandal for UBS. But the number needs to be seen in context. It barely amounts to four per cent of UBS’s $54bn of shareholder’s equity. By itself this is not large enough to break the bank – but the knock-on effects on UBS’s businesses might be – let alone the financial system. The global economy was wrecked not by supposed individual “rogue traders” but by a systemic and systematic failure to understand the exposures banks were consciously taking on – exemplified by UBS’s $50bn losses on mortgage-backed securities just a few years ago.