There will be much rejoicing in the Serious Fraud Office over the multiple guilty verdicts on Asil Nadir, 17 years after he fled the UK claiming that his business affairs were being investigated improperly. In returning to face a British court, Nadir appeared to gamble that time had reduced the potency of the case against him. It had not – not least because his conduct lost a lot of people a lot of money. His company, Polly Peck International – a household name in its day – will go down in the annals as a byword for dishonest business.

The 10 guilty verdicts far outweighed the two acquittals, finally bringing to an end a case that had long stood as a reminder of the SFO's lack of competence. And that is to be welcomed. But one high-profile conviction does not dilute in any way the arguments for reforming the SFO, which remain compelling. Last month, the Office had to drop its probe of the Tchenguiz brothers after the court found it had lost documents and overlooked key financial reports in what one judge described as "sheer incompetence". Then it reopened its two-year investigation into the collapsed hedge fund Weavering Capital which it had previously closed, saying there was no reasonable prospect of conviction, although a civil case had succeeded to the tune of £450m.

Most recently, questions have been raised about the SFO's failure to heed warnings about the fixing of the Libor rate at the time when the scams were being committed. There are older blemishes on its reputation, too, including the very modest penalty it extracted from BAE Systems over sales of radar to Tanzania, an apparent over-eagerness to cut deals and the tardiness of many investigations.

The high court has said the SFO lacks the resources to pursue complex economic crimes and needs more money – which may be so. But its new director, David Green QC, has his work cut out to restore its reputation and the soundness of its decision making. The successful prosecution of Nadir cannot erase the lengthy catalogue of concern. Unfortunately for the SFO, this signal victory has to be hailed as the exception that proves the rule.