RCD outlets have become available in recent years, but as Ragnar points out they tend to be quite pricey here, so they're not that widely used.
Contactum twin RCD socket This one is supposed to fit a standard 25mm (1") deep box, but to be honest it's enough of a squeeze getting a regular twin socket and its cable into one. British wiring accessories don't leave very much room.
[This message has been edited by pauluk (edited 03-14-2004).]