Airports with in / out bound inbalance

[davidjohnson6]

At the risk of thread creep...

Ballsout - APD works on the basis of final destination of the ticket (unless there's a 24h layover), not on where your flight from the UK lands first. Thus, a Manchester-Paris-Johannesburg trip costs the same as Manchester-Heathrow-Johannesburg.
One can of course buy a Manchester-Paris flight and a separate Paris-Johannesburg flight, but airline pricing usually has much higher prices for direct flights, and much reduced prices for itineraries involving a change.

Air France know that plenty of other airlines also offer 1-stop flights from Manchester to Johannesburg, but that only they and SAA fly Paris-Jo'burg direct so they can charge a premium for the non-stop flight. In the bizarre world of airline pricing, you may even find that a non-stop Paris-Jo'burg return costs more than a 1-stop Manchester-Paris-Jo'burg return.

Thus, unless you accept a 24h layover, a Manchester-Paris + Paris-Johannesburg is unlikely to save anywhere near the full value of the APD in the overall cost of the trip. In particular, the hassle of having to possibly collect one's bags at an intermediary airport before checking in again has a monetary value.

Yes, there are a few special cases where APD can be saved or a 24h layover might be desirable (e.g. American tourists who want to visit both the UK and France), but consumers generally will just put up with APD and the tax gets paid.