In 1984, London is the chief city of the province Airstrip One (which consists of the UK), which is a part of the superstate Oceania. Is there a reason why it's called Airstrip One?
I'm pretty sure it's a satirical jab at the perceived takeover of Britain by the United States. Just as in real life the US has filled Britain with its airbases, in the world of 1984 the entire country is seen as just a minor offshoot of US military power, a mere "airstrip" for the USAF to launch their warplanes from. We already know that the United States has taken over Britain; this is stated explicitly at the very start of Chapter III (War is Peace) of Emmanuel Goldstein's magnum opus:
The splitting up of the world into three great super-states was an event which could be and indeed was foreseen before the middle of the twentieth century. With the absorption of Europe by Russia and of the British Empire by the United States, two of the three existing powers, Eurasia and Oceania, were already effectively in being.
This would also fit with Orwell's generally anti-American attitude. 1984 has no mercy: it rips into the Soviet system of 'communism' but also into the west, the US and Britain.
As Mark notes in a comment, the name "Airstrip One" is also a clear reference to the way Britain is sometimes referred to in real life as an unsinkable aircraft carrier for the United States. (This phrase likely dates back further than the publication of 1984; one of Wikipedia's citations is to this Time Magazine article from 1950.)
The only other relevant quote I've found is this from Chapter 3:
Even the names of countries, and their shapes on the map, had been different. Airstrip One, for instance, had not been so called in those days: it had been called England, or Britain, though London, he felt fairly certain, had always been called London.
... which confirms that Airstrip One is indeed the country we now call Britain or England. But very little is known about life in the world outside of London in 1984, beyond broad generalities, so it's unlikely that there's a canonical answer to this in-universe.
In his 1943 article, “The Round World and the Winning of the Peace,” English geographer Halford Mackinder described Britain as a 'moated aerodrome' in the 'Midland Ocean' (ie the North Atlantic and surrounding countries, ie the US, Canada, France, and the UK).
It's been suggested already that the Ingsoc slogan in 1984 ('Who controls the past controls the future: who controls the present controls the past') was inspired by Mackinder's summary of his Heartland theory: 'Who rules East Europe commands the Heartland; who rules the Heartland commands the World-Island; who rules the World-Island commands the world' (in Democratic Ideals and Reality, 1919). Perhaps Mackinder's 'moated aerodrome' also served as an inspiration for 'Airstrip One'.