Rose 2 isdefinately not right! you dont need cables 2 & 3 for both lights to work from the one switch. whoever wired the rose is using it as a junction box for the other 2 cables. You need to find out what those 2 cables are supplying. check to see if any other lights only work when that switch ...
is the insulation on PVC cable affected by silicon sealants or cement etc? I have recently fitted main bonding from my gas meter and sealed the cable in the wall with a silicon based sealer?
when replacing a central ceiling light with say 8 low volt halogens is it better/easier to use a central transformer where the existing wiring is or use fitings with individual transformers? Also what is the technique for fitting if you cant access from above?
to be on the safe side use 10mm but put it thru a 40A breaker in the consumer unit, the shower will only pull high amps when set to scolding hot and in my experience this never happens. Then your well covered for correction factors etc.
