It was hotter in parts of Yorkshire overnight than it was in Istanbul during the day, and temperatures are expected to remain warm this week.
But there will be a north-south divide as things cool in Yorkshire while the south coast continues to bake.
MeteoGroup forecaster Callum Stewart said: "The highest temperature recorded last night was 24C at London City Airport.
"Temperatures eventually dropped around 4am but they remained in the high teens and low 20s.
"We can expect more warm and humid nights this week as the very warm weather will remain until Friday."
Temperatures will touch 30C again in Yorkshire today before dropping to around 15C overnight. There may even be the odd heavy shower.
Clouds will sweep in for the rest of the week with the odd sunny interval as daytime temperatures drop to around 20C.
Mr Stewart warned that while it may not be as hot, it is still important to take precautions against the sun especially as the Summer Solstice, the longest day of the year, is this week.
He said high pressure to the south of Britain will continue to drag hot air up from the tropics over the coming days.
In response to the extreme hot weather, Simon Bottery, director of policy at Independent Age, the older people's charity said: "Older people can suffer adverse effects on their health during the hot weather and can be more vulnerable to heatstroke, heat exhaustion and dehydration.
"We would encourage the elderly to keep as cool and as hydrated as possible, and stay out of the extreme heat and sun. "
Unusual levels of UV are also being recorded in the UK at the moment, which has prompted warnings that people should take sensible precautions in the sun.
The Met Office's forecast for Yorkshire:
A fine and dry morning with long spells of sunshine. More in the way of cloud developing through the afternoon with the odd heavy shower possible late in the day. A hot day once again, though refreshingly cooler on coasts. Maximum temperature 30C.
Any showers will die away through the evening leaving a dry night, though with a good deal of cloud spreading down from the north. Minimum temperature 15C.
Tuesday should be dry but with more cloud around compared to previous days and fewer bright or sunny intervals. Temperatures well down on those of Monday. Maximum temperature 21C.
Outlook for Wednesday to Friday:
Wednesday feeling humid with some heavy, possibly thundery showers developing. Thursday likely to be largely dry and very warm once again. Breezier and much fresher by Friday.