Staying and transiting in China

Hi, a double entry tourist L is ok to cover your trip.

Would a 72 hour transit permit cover it or should I get a double entry?

Actually, you can take advantage of 72 hour free transit in Beijing with British passport, as long as you have tickets leaving within 72 hour. But it is hard to say about the second transit via Shanghai, because a flight from HK -Shanghai -Combodia may not be considered as a direct transit, so you are advised to contact your airline or Shanghai Immigration Frontier inspection for more details: 0086-21-51105100