Fly to Shanghai from London but leave Shanghai with a changeover in Abu Dhabi?

That's okay if you are flying to Shanghai from a different country than UAE.

Yes - Understood. Apologies. I should have made it clearer. One option was I was looking to fly direct to Shanghai from London. Then on the way back choose a flight which stops off at UAE for changeover (but I am not looking to leave airport) for a few hours before flying onto London. Nothing I've read suggested that the country I am flying out to from Shanghai needs a minimum time there before going back to London. Thanks!

Doesn't matter. The Immigration only checks if your first destination outside China (including stopovers) is in a third country.