A Level 4 emergency could be declared as temperatures continue to soar across the country.
There is a 30 percent chance that Sunday will be the hottest day ever recorded in the UK, the Met Office has said.
On Monday, the Met Office issued an amber weather warning for extreme heat across parts of the UK ahead of further soaring temperatures this week.
But more action could be taken, with the UK Health Security Agency not ruling out a level 4 emergency.
Soaring temperatures are set to continue across the UK
Gareth Fuller
The UKHSA has said they cannot rule out a level four emergency
Andrew Matthews
According to the UKHSA, such an emergency is declared when the heat is so extreme that “illness and death may occur among the fit and healthy”.
A UKHSA spokesman said: “There's a possibility of a level four heatwave. If it gets above 40C, then it is likely to be a level four heatwave for the first time.
"I don't see how it couldn't be in those temperatures,” they told The Telegraph.
Network Rail has warned speed restrictions are likely to be in place this week on some parts of the network most affected by the hot weather.
While Fire services have urged people to have picnics instead of barbecues during the warm weather after a spate of grass fires.
The AA Driving School and RAC said motorists should carry water with them, start their journeys earlier in the day, plan their routes and check their vehicles before setting off.
Hampshire County Council also said it was preparing to deploy gritters to protect cars against melting roads.