As far as I know, my employment from my UK company will not cease so no P45. I am being sent on assignment to HK and will remain there for a significant amount of time (more than 1 year). I will likely not spend much time back in the UK as my family is in HK, no visa issues as I am a UK passport holder and I have dual citizenship with HK.
Having read this though, I'll probably seek some professional tax advice prior to heading out there. It's not for a few months yet so plenty of time.
Thanks for the comments