For March 2015 the best offers i can see are
Air China 15+ Hours £515.
Royal Brunei 17+ Hours £555
China Eastern 16 Hours £555
China Southern 17 Hours £580
Malaysia 16+ Hours £609
Cathay Pacific 14 Hours £610
Basically you pays your money and takes your pick.
There are more airfares on Cheapflights.co.uk ranging from £450 ish but long waiting times.