And unlike many places people go on holiday to the UK weather is humid whether it is very hot or very cold,
No it's not, certainly not all the time.
Humidity depends on the air mass currently effecting the area you are in ....and in the UK (like most places) that changes.
FWIW when a similar claim was made here last night a quick dip into the met (airport) reporting sites showed for example Nicosia was far more humid than Heathow yesterday evening - from memory at Heathrow the humidity was in the twenty percent range which isn't high at all and was much lower than it was Cyprus (and by chance by airports were at the same temperature)...
I think it's right to be concerned about the next 48 hours in the UK, it could be very unpleasant in places, I'll buy that in some ways the UK may not be as set up for hot weather as some other countries but I don't understand why there are frequent claims that the UK has some uniquely special and awful aspect to it's weather...