All three locations are often hot spots and are all located within close proximity of each other. Perhaps a combination of urbanisation & local terrain play a part? The heat equivalents to say Braemar & Altnaharra are for cold?
They do well with Southerly or SSE winds or calm (though St James park often wins in dead calm), my local one London City airport is good in Westerlies but not if there’s any Easterly component to the flow
I would say there is a long standing UHI influence at Heathrow, Northolt, St JP, Gatwick, City airport, the old Gravesend Broadness and possibly Kew although given how localised UHIs are and how much green is around Kew that one is more questionable. On the UHI maps from peak nights the strongest impact is in zone 1 central London, although St James park is a relatively cool island because of the string of parks in the area. UHI is overwhelmingly a night phenomenon but there are measurable daytime effects in mid latitude cities like London.
Topographically they are definitely hotspots as they are very low altitude, practically sea level, and sheltered by the downs but without being coastal. Gloucestershire airport is another one with similar topography in the West Country.
The other hotspot which annoyingly has no local weather station is the Medway valley north of Maidstone. On reanalysis maps always very hot as it’s at or close to sea level, sheltered to the South, West and East and close to but not right by the Thames Estuary. It’s where Chapel Down have their award winning Kits Coty vineyard which is just about the hottest in the country alongside the Crouch Valley vineyards in Essex.
Brockley, South East London 30m asl