Transfer Traffic is 34% according to CAA figures 2011, it's even higher now !
This from AIRPORT magazine January where I suspect The Spectator took their byline.
The most recent CAA figures for 2011 provide an interesting analysis of the UK's three largest intercontinental gateways Heathrow, Gatwick and Manchester. In 2012 Heathrow handled a total of 69 million passengers, by way of comparison over the same period, Manchester the largest long haul airport outside the South East handled 20million pax but curiously it is Manchester where the impact of APD is felt most. Unlike the South East most international long haul passengers using Manchester will either originate or terminate their journey in the NWest, some transfer to a short domestic flight to another UK destination, on that basis and using the Government formula all will pay APD.
Contrast that situation with the the South East and specifically Heathrow where a whopping 34% of total passenger numbers is purely international transfer traffic, the definition is important “International transfer passengers” are deemed to be those who simply fly in from one “international location” and then fly out to another “international destination”.
Had they been destined for another UK domestic airport they would of course have been subject to APD, but the simple fact is that this type of passenger totally escapes that tax and in effect pays nothing.
In effect, of the 69m pax who used Heathrow in 2011, a staggering 24million transfer passengers fell into this very specific category and paid no APD at all. This massive loop hole allows Heathrow to benefit from what in effect is a significant hidden subsidy compared to other UK airports.
At Manchester of course where domestic transfer traffic is significant but international transfer traffic is modest 87% of passenger pay a level of APD. This anomaly raises even more questions and impacts on the wider issue of the clamour for additional runway capacity at Heathrow. Often held up as a bastion of UK economic activity, it's really difficult to see what contribution the 24m tfr passengers are actually making to the UK economy, hopefully they might buy a burger between the jog to a international connecting flight but far from actually contributing to the UK economy by spending money like the humble businessman, holidaymaker or tourist using Manchester, all they actually appear to be doing is clogging up Heathrow's runways.