Here, SW of London, any North Sea influence is heavily modified so it has become humid and rather hot as opposed to a proper furnace like in recent years.
Even here, half a mile from the North Sea - and with an onshore breeze - the humidity has been the most noticable thing. Normally it tops off at 17 or 18C dewpoints in a hot spell, but this time 19 or 20C has been common. Indeed, the past few days it's hit 21C around lunchtime.
Even though the highs haven't been especially noteworthy here, the humidity has made it a sweat-fest. It really does make it feel much warmer than it really is!
(Last year in that hot spell Gusty mentions dewpoints started off around the 15C mark but quickly declined to single figures as the spell wore on. 30C with an 8C dewpoint feels much more pleasant than 26C with a 21C dewpoint!)