The Met Office says that the warmer weather, starting on Thursday, could reach a blistering 37C (98.6F) in some areas and is expected to last until Sunday.
This would mean parts of Britain could pass the threshold for an "official heatwave", which requires three days of temperatures over 25C (77F).
London and the South East are expected to see the highest temperatures on Friday, but northern areas such as Manchester and Leeds will also hit the low 30s.
Last week on July 31, the UK recorded the hottest day of the year and the third warmest on record, with the mercury rising to 37.8C (100.04F) at Heathrow Airport.
The Coastguard reported its busiest day for more than four years as it dealt with more than 300 incidents.
Ahead of this week's sunny spell, Gareth Morrison, RNLI head of water safety, said: "Our coastline is a fantastic place to spend time together as a family, especially when the sun is out and it's hot.
"But there are also plenty of potential dangers, especially for those who aren't fully aware of their surroundings and may be visiting a particular beach for the first time.
"We are advising everyone planning a visit to a beach or the coast to follow (the) beach safety advice."
A spokesman for the Met Office said there was a "low chance" that last week's record temperature would be beaten again but that large parts of the country would see "four or even five consecutive days of incredibly warm temperatures".
"It is the result of southerly winds moving from Europe and parts of northern Africa, which will push the temperatures up," he said.
He added: "It's pretty unusual to get two successive events like this within a week of each other with such high temperatures."
The heatwave conditions are expected to last until Sunday before cold air moves in overnight, but conditions are expected to stay "hot and humid" next week with "chances of thundery showers".
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