Temperatures reached 24.8C in Porthmadog, north Wales, beating Sunday’s previous record of 24.4C in Plymouth.
Many in southern and western parts of the country also enjoyed sunny weather well over 20C during the first two days of the bank holiday weekend.
Both Scotland and Northern Ireland also recorded their highest temperatures of 2023 so far, with the mercury climbing to 24.2C at Tyndrum, Stirling, and 24.1C at Castlederg, County Tyrone, respectively.
Met Office senior meteorologist Rachel Ayers said: “We may still see higher temperatures over the next hour or so.”
Met Office meteorologist Alex Deakin added that high pressure would continue to dominate the country this week as a “cold front is shifting away”, bringing more fine weather.
On Thursday, temperatures are forecast to reach 22C in Glasgow, 19C in Belfast and 20C in London and Plymouth respectively.
Between Thursday and Saturday, the Met Office has also predicted warm sunshine with some cloud along coastal areas.
In its long-range forecast, the Met Office predicts the potential for “very warm conditions” for early June – the official start to the meteorological summer – particularly in sheltered western and northwestern areas.
Dry and settled conditions are expected for much of the UK, the Met Office says looking further ahead into next month.
Although cloud cover may affect the northeast and eastern counties, temperatures are forecast to warm up away from windward eastern coasts. There will also be light winds and the possibility of moderate breezes in the far south of the country.
The UK recorded its highest-ever temperature in July 2022 in Coningsby, Lincolnshire at 40.3C.
The days-long heatwave sparked government heat safety warnings for the elderly and vulnerable people to stay inside and for people to work from home where possible.
Drought was also declared in a number of counties with hosepipe bans lasting many weeks and in some cases months.