In one sense, the arrest of Nicolas Sarkozy in Paris this week can be seen as just the latest, albeit very high-profile, example of a continuing international investigative effort against financial abuse in Europe's political processes. Senior politicians have faced corruption grillings in Germany, Italy, Spain, Greece, Ireland and Britain in recent years and in many cases paid the price. In France itself, the socialist budget minister resigned last year after the discovery that he held hundreds of thousands of euros in Swiss and Singapore bank accounts. In that sense, the arrest of Mr Sarkozy – who denies all the charges – may not say anything unique about either France itself or the former president's right-of-centre political party.

Yet the arrest is surely a milestone in both of these contexts. Past French presidents were plagued by corruption allegations during and after their terms of office. None, however, was subjected to the 15-hour police station detention to which Mr Sarkozy was subjected this week. None was placed under notice of investigation for "active corruption", as Mr Sarkozy has now been. This could either mean that the charges – which include allegations of accepting huge campaign donations from the former Libyan leader Colonel Gaddafi in 2007 – are far more serious than those that dogged Presidents Giscard, Mitterrand and Chirac. Or it could mean that a bar has simply been raised, and that French public life has begun to get more transparent than it was in the past – a possibility also signalled by the recent treatment of François Hollande's private life.

Realistically, the arrest might already mark the end, or the beginning of the end, of Mr Sarkozy's time in the top rank of French politics – which would become certain if Mr Sarkozy ended up with the 10-year jail sentence that is the maximum punishment for the corruption charge. It comes just as the former president was beginning his manoeuvres to regain control of the Gaullist UMP later this year, which could be a stepping stone towards a credible presidential run against Mr Hollande in 2017 and a possible Sarkozy restoration.

Both the arrest and the timing are helpful to the currently unpopular Mr Hollande, which inevitably raises suspicions on the right. Hoping to mirror Mr Chirac's landslide win in 2002 against Jean-Marie Le Pen, when the socialists were in disarray, Mr Hollande would probably prefer a second-round run-off in three years' time against Marine Le Pen rather than against a resurgent Mr Sarkozy or a lesser UMP personality such as Alain Juppé. So the consequences of this week's events could be very large and very damaging for France. That's no reason for the investigation not to take its course. But the stakes are very high, particularly at a time when Europe – including a febrile Britain – needs a stable and outward-looking France.