Dan, don't be ridiculous. Why would anyone want to trade a career of chaos and misery for the opportunity to live and work in/near your home, with a recognised first world airline with robust labour law protections and exciting career path (not to mention hosties you can actually tell a joke to)? Sorry man, but you are going to have to do waaaaay better than that to get me to give up the pollution, dirt, non-rostering system, joke rosters, crowds, shoebox apartments, cultured locals and all the other wonderful aspects of living in HK. Don't forget, by staying with CX, you are assured that the management will continually demonstrated respect and gratitude towards you for the sacrifice you make. If that doesn't convince you, then being able to put away thousands of $$$$ a month into savings should surely swing it. Oh, wait....
Grass is always greener syndrome. Give me the polite, respectful asian cabin crew any day of the week (careful with the kind of jokes you tell the crew in western airlines, very easily offended). Give me the vibrant expat scene in HK over the dreary miserable culture back home. London is great if you like rain, high taxes and being treated like a terrorist by staff security every day despite doing a million background checks (no liquids >100ml captain).
Sorry if you're miserable in HK, but life as an FO in BA won't be quite the western civilized utopia you're dreaming of. And you will certainly be financially less well off too, have you looked at rental prices in London recently? Food for thought.