British citizan/HK born Chinese with 回鄉證 - flying direct from London to Chengdu or need to go via HK

I am British citizen with UK passport. I was born in HK and also have HK ID and 港澳居民来往内地通行证. I also have HK 特區護照. I am planning to fly directly from London to Chengdu and back from Shanghai. Do I need to travel via HK both ways? Would airline check-in staff in London allow me to board flight to China with just the HK identification documents or would they let me board the return Shanghai-London flight with UK Passport that does not show a China tourist visa? Again, do I need to come home via HK?