Originally Posted by NickB

Actually, you are right that I forgot to untick "allow airport changes" in my search, resulting in mixed itineraries. The corrected table is as follows:

Route Airline Cost
PEK-FCO SU £633
PEK-CDG SU £647
PEK-LHR SU £656
PEK-CDG CZ £663
PEK-FCO HU/SN £673
PEK-CDG AY £678
PEK-LHR OS £680
PEK-CDG CZ/KL £694
PEK-FCO AF £703
PEK-FCO TK £707
PEK-CDG OS £708
PEK-FCO LX £709
PEK-FCO AY £711
PEK-CDG LX £712
PEK-LHR LX £714
PEK-FCO MU/AZ £717
PEK-CDG AF £728
PEK-FCO LH £728
PEK-CDG LH £734
PEK-CDG KL £746
PEK-LHR LH £746


It still shows the same thing: that there is no clear pattern of fares to London being increased by the amount of the APD. This is true across the board and also on many individual airlines.

For instance, SU cheapest fares to London are indeed more expensive than to Paris but by a mere £9. Once you take into account exchange rates variations, this is pretty much indiscernible.
Conversely, the lowest OS fare on PEK-LHR (£680) is lower than their lowest fare on PEK-CDG (£708).
LX charges £709 to FCO, £712 to CDG and £714 to LHR, so pretty much the same. Ditto for LH at £732, £734 and £742 respectively. All in all, thus, there is no evidence of systematic higher fares to London due to APD.

You are quite right that CZ does charge substantially more to LON than to CDG. It seems that CZ does not seem to follow usual market pricing principles and seemingly has a set fare for "Europe" regardless of what the demand is to various destinations. But what this shows is that it is dangerous to draw conclusions based on just one airline, especially an airline which has pricing practices that seemingly run counter to normal market practices.