Etihad used to run an A343 from the North Terminal and Qatar an A333 from the South, later the North, however both moved to consolidate London operations at LHR. The only way they'd do a Cathay and return I think is if they couldn't grow any more at LHR. However both a re growing, Etihad are slowly moving to all A380 and Qatar have managed to source a few more slots as well as upsizing from A330 / A319 (no really) to A380.
Etihad left end of Summer 2006, Qatar end of summer 2011. Emirates do really well but they are quite literally exceptional.