This reply from the Met OfficeUKMO The Meteorological Office is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy regarding air temperatures from airfields being contaminated by aircraft activity makes me smile when I think back to some of the stations I worked as an observer. Even from more than 100M away or more an English Electric Lightning could generate some heat, and noise, as it was warming up on the taxiway! To compound this possible contamination the Met Office today use very sensitive thermometers in their AWSAWS Automatic Weather Station, and not the mercury thermometers that were around when I was an observer. There are a lot of well sited AWS stations in the UKUK The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and Northern Ireland., but most of the AWS at airfields such as Heathrow are pretty poor. Take a look at these aerial images of the siting of the enclosure at RAF Waddington in Lincolnshire for instance, a key UKMOUKMO The Meteorological Office is the United Kingdom's national weather service. It is an executive agency and trading fund of the Department for Business, Energy and Industrial Strategy key climate stations.
As you can see although the Stevenson screen enclosure does sit on a triangle of grass it’s surrounded by two car parks and the perry track, where aircraft taxis to and fro to the main runway at takeoff or on landing.
If you’re interested to find out more about UKMO observing sites check out this link.