On Sunday, Glasgow hit 22C (55.4F) compared with highs of around 25C (77F) seen in Edinburgh and the Lothians. In the evening the temperature dropped in both cities to a cooler 15C at midnight.
In Istanbul today temperatures did not climb higher than 23C.
London saw the mercury rise to a sweltering 31C during the day and a was sitting at 24C during the evening.
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.”
During the day temperatures will be highest in London, with much of central and south-east England also enjoying high temperatures.
Mr Stewart added: “We will probably see the highest temperature in the west London area today, which will peak at 32C (89F). “
The weather expert warned that it is 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.