In a gentler age, before terrorists made aviation their preferred arena, Britain's leading airports were tourist attractions.
As Heathrow and Gatwick grew up in the 1950s and 1960s, they promised a brave new world of global connectivity – and provided somewhere for a family day out. Probably more people came to gaze upon the destination boards, with the exotic promise of Biarritz, Baghdad or New York, than ever actually flew.
Anyone excluded from foreign travel by the outlandish fares then charged by the airlines could nonetheless mingle with the rich and famous, sipping tea at Fortes 24-hour Bar and Buffet and dreaming of foreign airfields. Day-trippers were denied access only to the inner sanctum beyond passport control, where departing passengers could buy a bottle of gin for 14 shillings from Fortes Duty-Free Liquor Shop.
Half a century on, air travel has become democratised. We are (almost) all passengers now. Airports in the London area alone will handle 140 million travellers this year, making it the world's leading aviation gateway. But modern airports are like prisons and hospitals: most people would prefer to avoid them altogether, and, once inside, want to get out as fast as possible. An airport is just an uncomfortable, undignified means to an end.
Or is it?
Since Heathrow and Gatwick became rivals five years ago with the break-up of BAA, tens of millions of pounds have been invested in new shops to boost the pre-flight offering. At the same time, retailers recognise that a location adjacent to a runway at a London airport is the fastest way to reach a global audience.
For practitioners of the retail arts, there are many challenges. Passengers are typically tired and stressed after the trip to the airport, whether that involves the M4, the Piccadilly Line from central London or a long-haul flight from Mumbai. They may be fixated on a single "distress" purchase: Boots is always front of house for last-minute personal needs, while among the fastest-moving lines at Dixons are connectors and chargers for tablets and telephones. (Incidentally the Dixons brand, first seen "airside" at Heathrow 20 years ago, has long disappeared from the High Street but lives on in Britain's airports.)
But airport merchants also enjoy advantages. The typical passenger is happy to spend freely before they step aboard and fly somewhere exciting (or home to Ohio), because shopping is an alluring way to kill time. They have probably allowed plenty of time to reach the airport; when they find motorways unblocked and the security search painless, they become people with plenty of "dwell time" on their hands. Passengers can't wander back to the car or the bus stop when they've had enough. The only way out is on an airliner. Add in the travellers who need to buy presents for family and friends and will pay whatever it takes to assuage the conscience, and it's no surprise that seven out of 10 Heathrow passengers buy something (a larger proportion than use the loos).
"When people are here they are in a very different mind-set," says Max Vialou-Clark. He is Heathrow's retail services director, and as such has to cater for the most diverse range of shoppers in the world.
"They want an experience, places that entertain and amuse them and they're prepared to upgrade." That explains the long-standing presence at Heathrow of premier-league brands such as Harrods. But when the new Terminal 2 opens in June, the average British traveller may be surprised by the familiarity of the retail offering.
John Lewis has never knowingly opened a small shop, nor a store at an airport. At "T2" the partnership will be doing both. The Heathrow outlet will be one-tenth the size of its smallest existing department store in Exeter. The main target is not the British traveller who needs to run one last retail errand on home turf before encountering those funny foreign shops, but international passengers. "Even if I'm only a connecting passenger – I want to feel as though I'm in Britain," says Max. At T2, 40 per cent of the shops will be British brands, such as Cath Kidston, as opposed to international labels; at Terminal 5 the proportion is 25 per cent.
The average shopper at Heathrow spends £39, which adds up to £1.8bn in a year. The airport benefits from the fact that most of its passengers are flying long haul. Not only do nationalities such as the Japanese, Brazilians and Chinese have a higher propensity to spend than do Europeans – they also typically allow a lot more time before their flight.
Gatwick does less well from shoppers, who are predominantly heading for destinations in Europe. Research at the Sussex airport says travellers are demanding "a more premium and stronger mainstream offering of both national and international brands". And what does that mean? New shops including Ted Baker and the largest Zara airport store on the planet.
Spencer Sheen, who is head of retail at Gatwick, claims the £40m project "takes airport shopping experience to a whole new level."
A new arrival at the departure lounge is Snow+Rock, bringing outdoor gear such as The North Face to the South Terminal. The firm's marketing director, Kevin Young, says: "We look forward to realising the potential of a tightly focused product range." Loosely translated, that means you'll find lots of jackets but not the kit for a Himalayan expedition. This is partly because profits per square foot are higher for clothing, but also because Swiss Army knives and ice axes would not get through security. Anything sold "airside" at an airport, from a copy of the Independent paper to a bottle of Smirnoff Gold complete with real gold flakes, has to be screened just as passengers are.
An airport so good you won't want to take off: that is the hope of both Heathrow and Gatwick. But Max Vialou-Clark says he will understand if you bypass the retail opportunities and go straight to the gate: "There's a single primary reason that you're here and it's not shopping. You and everyone here is boarding an aircraft."