I have just looked at a few automatic online stations which have the
following maxima

Clifton 34.8°C
Bishops Stortford 33.6°C
Cambridge 36.6°C and 37.2°C (the latter station is on a roof)
Peterborough 36.2°C
Crowborough 29.8°C
Crawley Down 35.3°C
Aldershot 33.8°C (aspirated screen)
Herne Bay 35.7°C
Morden London 34.9°C
Shoreham Beach 26.8°C
Pitsford Hall 32.4°C

My maximum was 35.4°C

Alan