The T+Cs for mainland carriers aren't good. Once they have you - that's it! China Southern recently won a court case to recover the training costs from some of their pilots who jumped ship. I can't remember the amount, but it was hundreds of thousands US dollars!!!!! Also, I suspect holding a UK passport will not be helpful. These companies do have foreign nationals flying for them, but on contracts.
IMHO, your best bet is to build a few hours and apply to Cathay or Dragonair. With the right to live in HK, you can apply to be a direct entry local contract Second Officer with Dragonair with 250 hours, or 200 hours if doing an integrated course approved by the HK CAD. I suggest you contact them now to sound them out.