Forecasters have predicted the hottest weekend of the year so far, with temperatures due to hit 32C (89.6F).
The Met Office is warning people to take precautions in the sun
Parts of the UK are expected to reach 30C on Saturday and 32C - a 2005 high - on Sunday, exceeding forecasts of 30C for Mediterranean coastal resorts.
The Met Office has warned fair-skinned people of a very high sunburn risk, while the RAC has urged people to plan journeys to avoid long queues.
The year's highest temperature so far was 31.9C (89.4F) in London on 27 May.
Parts of England and Wales are due to enjoy the warmest weather, while temperatures should reach 28C in Scotland. Northern Ireland will be cooler.
A PA Weather Centre spokesman said: "We are seeing this hot weather because of warm air from the south and south-west.
"These temperatures will really make it feel like summer."
'Pressure on roads'
But an RAC spokesman warned: "Many people will be hopping in their cars and heading for the beach and other outdoor attractions.
"This could put pressure on the routes leading to the most popular weekend destinations, particularly around coastal resorts - people should plan alternative routes if necessary and give themselves plenty of extra time for their journeys."
Bookmakers William Hill have slashed the odds on the UK's record temperature - 38.1C (100.6F) - being beaten this year.
From 16 to 1 in January, the odds have been cut to 5 to 1.
The hot weather is predicted to cause thundery showers on Sunday and Monday, leading to slightly cooler weather.
A Met Office statement read: "With soaring temperatures, concerns rise for people's wellbeing.
"The sun is at its strongest at this time of year and sunburn is a real hazard."
During the heatwave of 2003, some 27,000 people across Europe died as a direct result.
In the UK there were 2,000 deaths caused by the heat - 85% of which were people aged 75 and over.
Health experts say it takes just two consecutive days of heatwave temperatures to have a significant effect on health.
After the 2003 heatwave, the government instituted a warning system which identified four levels of risk.
Currently, this weekend is at level one, the lowest risk level, where general vigilance is urged.