Why do airports in the UK have so few runways? Almost all of the major airports in the United Kingdom are single-runway (or functionally-single-runway) installations, with only two of the very busiest (Heathrow and Manchester) having as many as two runways (although Heathrow has a third under construction).

(In addition, even for the three major UK airports that have two runways, the two runways are always a parallel set, with no provision made for crosswind operations.)

This is - with few exceptions - far fewer runways than would be normal for airports of their size.  Taking the seven airports in the UK with more than ten megaemplanements in 2018 and comparing them to similarly-sized airports elsewhere:


Heathrow (two runways, with a third under construction) v. O'Hare (seven runways, with an eighth under construction)
Gatwick (two [functionally one] runways) v. Newark (three runways)
Manchester (two runways) v. la Guardia (okay, two runways)
Stansted (one runway) v. Baltimore-Washington (two air carrier runways1)
Luton (one runway) v. Calgary (four runways)
Edinburgh (one runway) v. Norman Mineta (two runways)
Birmingham (one runway) v. Raleigh-Durham (two air carrier runways1)


Having so few runways not only increases congestion and severely limits the number of flights that can use the airport without infringing on safe separation distances between aircraft, but also poses the risk, for the four single-runway airports,2 of an unserviceable runway (for instance, due to snowplows, potholes, trespassers, flocks of birds, wayward deer, or a disabled aircraft) shutting down the entire airport, potentially for a prolonged period of time.

Why do the UK's major airports have so few runways compared to the norms for airports of their sizes?



1: Plus one general-aviation runway each for Baltimore-Washington and Raleigh-Durham.

2: And, to a lesser degree, for functionally-single-runway Gatwick, as its emergency backup runway is close enough to the main runway for a single debris event to potentially affect both.
There are perhaps 101 non aviation-related reasons why the UK does not have larger airports, such as space consideration (we're only a small island!), politics (NIMBY!), civil engineering (Airports are commonly near urban centres and are often surrounded).

However, the most aviation-related related reason I can think is that we just simply rarely need cross runways. If you look at most large airports in the UK their runway(s) are east-west(ish). The reason for this is over 70% of the prevailing wind direction in the UK is West or SouthWest. 

In addition, we rarely have extremes of wind - those exceeding the crosswind capabilities of common commercial airliners. Heavy snow is even rarer. I can probably count the number of times a runway at a large airport has been closed due to any of the reasons you mention in the last 20 years on two hands.

Bottom line; it's just not necessary. There is no socio/political/weather climate to warrant it.