Thanks Sven!

Castorama also has something else that I have been thinking of asking about, namely single width, double pole circuit breakers.

Look e.g. at this:
http://www.castorama.fr/boutique/sku/sku.jhtml?elementId=Casto824440&productId=CastoEL0205

Does anybody know if these work with busbars? Or if they exist in a 4 pole version?