We kept our house, and are renting it out. Loads of stuff is in storage (our company pays for it, maybe yours will too).
Your companies' expat package will affect your decision, but we didn't want to sell a house we'd (just barely) finished renovating. Of course, property values are rising where we bought... so that's another reason to hang on. And we ARE going back.
Anyhow, I'd keep the house and start looking for a really excellent agent to manage it while you're away. I wouldn't leave it empty; rent it out! The damage (reasonable, sane) tenants can do is pretty minor compared to the mould that can grow in a shut-up place, nevermind possible squatters.
Of course, we may end up having to rent a place for a while when we go back, depending on the tenants' contract. Our company will subsidise our rent if that happens.
Buying in London is an insane prospect at the moment. Some will disagree! Not only that, but we were sent here for three/four years... only to be told that we're moving to Germany after the first year. Don't know if your company is more stable/less demanding/however you put it, but I'm VERY glad we didn't try to buy here.
So, I'd begin with a close look at your expat package.