Pailton Radio Station is a civil facility owned and run by a UK PLC which enjoys no special treatment as far as Health and Safety legislation goes. In addition it's a place of employment for a number of people which brings in extra responsibilities. I think you can be fairly sure that it complies with all legislative requirements especially as the people who work there are rather well placed to understand all about RF radiation and how to measure it and would be unlikley to put themselves at risk. Of course if you are a member of "they would say that wouldn't they" club you can always commission your own survey.
Both VHF and UHF are used in UK Air Traffic Control and I'd expect to find aerials for both on the mast but the majority will be VHF and personally I could never tell the difference without looking at the label.
I can't tell you who the site sharers are because I don't know. There are some obvious suspects looking at the aerials in the photos and the Ofcom site finder site will probably give you both frequency and signal strength if they are using the site.