Can anyone kindly check the below itinerary please?

Holding UK passport

First I have booked a returned (round trip) flight from London-Shanghai-London with British Airway for 2 weeks.

I intend to fly to HongKong after arriving in Shanghai within the 144 hours. After 1 week in Hong Kong I will then fly back to Shanghai for a couple of nights before jumping back on my return flight to London.

So in theory my route is as follow:

London-Shanghai-HongKong-Shanghai-London.

1) Does the above route allow me to travel visa free and make use of the 144 hours TWOV?

Essentially it’s
Route 1
london-Shanghai-HongKong

Route 2
Hongkong-Shanghai-London

2) When I go and check in at London Airport Terminal 5 with British Airway will the staff deny me boarding and say your return flight is London-Shanghai-London. You need a visa!

What I intend to do is book a separate flight from Shanghai-HongKong-Shanghai so will the staff take this into consideration and accept that Shanghai is a transit only destination and not my final destination?

3) I did input the details on Timatic with Hong Kong as my final destination with China as a transit so that part seems fine. I’m just more worried BA staff at London Airport will not accept the internal separate flight I will have booked from Shanghai to HK and Shanghai.

hope that makes sense!

Thanks all