The British group of 4,500, the largest in attendance, is moving from a camp site at Saemangeum to Seoul, the Scout Association confirmed.
The US and Singaporean teams are also pulling their members out of the event.
South Korea’s government said it was sending 60 more medics and 700 service workers to maintain the toilets and showers, with many countries staying at the site for the next week.
The jamboree, described as the world’s largest youth camp, gathers Scouts from around the world every four years, each time in a different country.
Most of those attending are aged between 14 and 18, and 155 countries are represented in South Korea.
This is the first jamboree since the pandemic and is due to run until 12 August.
Coaches of British teenagers have started arriving back in Seoul - about 120 miles (197km) from the campsite - and they will spend the next week in hotels.
The UK Scout Association said young people and adult volunteers had begun “settling into their accommodation” and the Jamboree experience would continue in the city before returning to the UK on 13 August as planned.
The BBC has been told that some scouts are sharing five to a room, while up to 250 are sleeping in the ballroom of one Seoul hotel due to a lack of available accommodation.
This is the best summary I could come up with:
South Korea’s government said it was sending 60 more medics and 700 service workers to maintain the toilets and showers, with many countries staying at the site for the next week.
One of the UK team told BBC’s Seoul correspondent Jean Mackenzie the decision to pull out was not based just on the extreme heat but was also down to the facilities and food.
The UK team monitored conditions for a number of days, they said, giving the organisers the opportunity to improve them, but had lost confidence they could keep everyone safe.
“By all accounts the heat is intolerable and adults and kids alike can’t continue there,” she said, adding that her family were “lifelong Scout people” and that the leaders had been “absolutely phenomenal”.
South Korean Prime Minister Han Duck-soo announced that aid was being sent to the site amid criticism from some that authorities failed to plan for extreme heat.
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