Thursday's high surpasses the 32.6C recorded in London on Wednesday.
It comes after a major incident was declared in Bournemouth, as thousands of people headed to the Dorset coast.
Dorset Police urged people to stay away after reports of traffic gridlock, anti-social behaviour, fights and overnight camping.
People have also been cautioned to stay safe by Public Health England and the Met Office.
An amber level three heat-health alert, issued by the Met Office, was extended on Thursday to take in Yorkshire and the east and south of England as well as the West and East Midlands.
That means people should drink plenty of fluids, avoid consuming excess alcohol and "look out for" young children, babies and those with underlying health conditions, the Met Office said.
Public Health England (PHE) echoed the Met Office advice, saying older people, those with underlying health conditions, and very young children were all more at risk from the "exceptionally hot weather forecast this week".
Both Wales and Scotland also recorded their hottest days of the year on Thursday.
In Wales, the temperature reached 30.7C at Gogerddan, near Aberystwyth, beating the previous high of 30C from Wednesday. And in Scotland, a high of 30C was recorded in Prestwick.
In Northern Ireland, a high of 25.5C was recorded in Aldegrove.
The Met Office also warned of high levels of UV radiation. By 13:00 BST, UV radiation was high or very high across the UK, with the south of England recording the highest levels.
The highest recording for UV radiation in the UK was in south-west England, which reached 9 on the UV index, the Met Office said.
The index goes up to 11, with a recording of 3-5 described as moderate, 6-7 as high, 8-10 as very high and 11 as extreme.