Technically it isn't 37% of passengers using LHR - that percentage is derived by counting every transit passenger twice, once on arrival and again on departure.
If you're confused by that, you're in good company - earlier this year the GLA's Transport Committee asserted that "There are disputes about the extent to which Heathrow is operating as a hub airport. It is not clear how many of Heathrow's passengers are transferring with estimates ranging from 22 to 36 per cent".
http://www.london.gov.uk/sites/defau...%202013%29.pdf (Page 5)
It turned out that there is no "dispute" - they simply didn't understand that there are two different ways of calculating the proportion of transfer passengers.
Doesn't matter, it's generally accepted as about 30% (compared to 70% at AMS). What matters is that transfer pax make some routes viable that otherwise would not be, and that expands choice for all pax.
Wouldn't trust any of the nonsense that comes out of the GLA/TFL as far as aviation/airport policy is concerned. It's also very biased in one direction. The mayor's aviation adviser isn't actually an aviation expert.
Moreover, despite mayoral delusions of grandeur, aviation
policy is beyond the remit of the GLA, it's not a local government function. More public money being wasted?