SriLankan Passport holder and British family

This is a very simple situation for both UK and Sri Lankan citizens. Your layover will be covered by 24 hour visa free transit scheme and you definitely do not need any kind of visa. Since your layover time is relatively short, you will not attempt to exit the airport, so you will just walk from one to the other gate and you will not be a subject to immigration and customs controls. Also, you do not have to fill out any forms and perform any formality. In reality the only formality you will accomplish will be to declare at the time of check-in in both London and Kuala Lumpur that you will fly to your final destination using 24 hour visa free transit scheme via China. Have a nice journey.

Hi Borut - thank you so much for taking the time out to respond. I'm sure every single person reading this will appreciate all the effort you've put in place!! Thanks again!