Unprecedented levels of traffic are expected as people swap the city for popular beaches and beauty spots.
Many parts of the country are on track for a heatwave with temperatures set to reach 32 degrees, the Met Office has said.
Half of drivers are planning their getaway by car and roads are heaving, according to reports.
Beachgoers are already flocking to the sea in Brighton while more than 150,000 people are expected to visit Bournemouth and Dorset this weekend amid highs of 26 degrees.
It is thought 97 per cent of a total 16,000 hotel rooms and 30,000 beds have already been booked for Saturday in the town.
Tim Seward, chairman of the Bournemouth Area Hospitality Association, said that the surge is due to pent-up demand caused by overseas travel restrictions.
“Any summer day where the sun is shining is obviously going to be busy,” he said.
But this year there is pent-up demand because people cannot go abroad.
He added: “We are expecting hotels will be fully booked by Saturday.”
Those braving the heat in London can expect highs of 31 degrees, higher than Ibiza predicted 29 degrees on Sunday.
Parks, lidos and watersports centres will likely be packed across the capital with one exception being the Hampstead Heath ponds which remain closed after Monday’s flash floods.
Super Sun Weekend
Warnings about the extreme heat have been issued by both medical authorities and vets, urging people to keep the vulnerable and animals safe.
Even areas further north including Hull and Newcastle are expected to reach the mid to high 20s as the weekend progresses with temperatures “building day-on-day”, according to the Met Office.
The criteria for an official heatwave is three days of sustained high temperatures but this can vary across the country.
Met Office meteorologist Andy Page said: “The extension of the Azores high is the principal reason behind the UK’s current weather pattern, which will see much of the UK reach heatwave thresholds over the weekend and into early next week.
“High temperatures will remain in the forecast well into next week, but there’s a risk of isolated heavy showers in the south of the UK on Monday and Tuesday, although it should be largely fine for most areas.”
A heat-health warning was issued by Public Health England (PHE) ahead of the predicted extreme temperatures.
PHE advised people to look out for those who may struggle to keep cool and hydrated, such as older people and those who live alone.
It follows a week of flash flooding in the south east of England, causing disruption to transport in London.
Germany and Belgium also experienced extreme flooding this week which have lead to dozens of deaths.