On September 15 2008, Lehman Brothers filed for bankruptcy protection, tipping the world into a financial and economic crisis of nearly unprecedented magnitude. Four years and much regulatory work later, financial markets have become a safer place.

Yet Europe’s efforts to draw the right lessons from the crisis will have amounted to little if we do not get the next step right – the creation of a truly effective European banking supervisor to enforce a robust single rule book for the sector.

The key lesson of the crisis, one sadly confirmed by the recent Libor scandal, is that self-regulation and light-touch supervision just do not work in the financial sector. Without adequate rules and careful policing, the interests of individuals and those of the system will invariably diverge. Left to its own devices, the market will self-destruct.