Temperatures in parts of England and Wales have topped those in Spanish resorts as the hot weather continues.
The South East hit heatwave conditions on Sunday
Monday was the hottest day of the year, with a temperature of 32.7C (90.9F) recorded at Heathrow Airport in London.
Unbroken sunshine and temperatures of 33C (91F) hit the south of England, higher than in Ibiza - 31C (88F) - and the Canary Islands - 27C (81F).
Scotland will see rainy patches while temperatures elsewhere could beat July records on Wednesday, say forecasters.
Temperatures in Aberdeen reached an all-time record 29.8C on Monday, surpassing the previous one of 29.6C.
The BBC Weather Centre said it expected London temperatures to reach 37C (99F) on Wednesday, breaking the July record of 36C (97F), seen in Epsom, Surrey, in 1911.
BBC weather forecaster Tomasz Schafernaker added there was a "10% chance" the UK's all-time record of 38.5C (101F), recorded in August 2003, could even be beaten.
"On Tuesday and Wednesday, temperatures in the Midlands will rise to around 34C and 35C so already there will be some local records broken for July," he said.
He said temperatures would ease off to around 30C in the Midlands and South East on Thursday and Friday.
"It will be a little bit cooler, but the hot air will remain and we do not expect a big freshening up on the way," he said.
Mr Schafernaker added that humidity could make temperatures feel warmer in some areas on Thursday.
Meanwhile, the Met Office recommended people stay hydrated in the heatwave conditions.
Spokeswoman Sancha Lancaster explained heatwave conditions varied between regions.
In the South East, it means temperatures must reach 31C (88F) for two consecutive days, with night temperatures reaching 16C (61F).
"The night temperatures are important, because it means the body isn't able to cool down," she said.
"For the general public the most important thing is to keep properly hydrated.
"We also advise people to try and stay cool, by ways such as using fans, and the warning also means people should be sun aware and take care by using lotions and wearing hats."
The Met Office's Solar UV Index is six or seven for most of England and Wales for the first three days of the week.
A seven rating means the risk of skin damage for fair-skinned people who burn is very high, for those who are fair and tan it is high, and for those who are brown skinned or black there is a medium risk of burning.
Transport for London repeated its advice to passengers to carry water with them on the Underground.
"While you are in the Tube, if you feel ill, or feel that you are overheating, then you should get off at the next station and maybe go above ground to get fresh air," a spokesman said.
North-east England had around a 70% chance of meeting its heatwave conditions, said the Met Office.
The region must be 28C (82F) for two days, with a night temperature or 15C (59F).
Meanwhile, the BBC Weather Centre in Leeds said the record July temperature for the city was likely to be broken in the next two days.
The record which was set in July 1989, is 31.1C. The forecasters said the city may reach 32 or 33C. The all-time record for the area is 34.4C, set in August 1990.