Originally Posted by
zoqfotpik
Certain nationalities are eligible for transit in China without visa aka TWOV. In PEK, you are allowed up to 72 hours as long as your itinerary takes you to a "third country". HKG is treated as a separate country. In this case, you can do LHR-HKG-PEK-LHR or LHR-PEK-HKG-LHR, but not LHR-PEK-HKG-PEK-LHR without a visa.
Can I ask why the latter isn't valid? Surely it's a return flight ... LHR-PEK-HKG (valid for 72-hr visa) and then HKG-PEK-LHR (valid for 72-hr visa).