Note the work to be done to today's regs emphasis. Wasn't aware that only the extension need comply, and is an officially acceptable practice - thought that was me being clever - ducking and diving regsROTFWLif you are getting told off for it you have to go with what your scheme says although this seems to say differenthttp://www.esc.org.uk/forum/forum_ed_thread.html
EDQ3
In the answers it states the extended part of the circuit must be RCD not the existing.