The Candy Empire (as it is called) isn't that good. I'm from the UK and didn't recognise much of the chocolate in there, but you could always ask them and see if they'll get some in.
Mustafas often get in UK chocolate. I've had bounty bars and cadbury's from there. Last time I was there, a few weeks ago, I asked and it was all on order so it may be in by now - it sells out fast though.
Also you sometimes get UK chocs in the more popular with expat supermarkets, such as the ones at Tanglin Mall, Paragon, Raffles City etc. Not sure if I've ever seen Revels etc, but you never know.
Happy hunting.