Britain on Monday issued an extreme heat warning, with temperatures predicted to hit more than 30 degrees Celsius (86 Fahrenheit) across large parts of England and Wales.
Forecasters said the warm weather would remain for much of the week, particularly in southern and central England and Wales, with peaks of 33C possible in southeast England on Tuesday.
Temperatures were still several degrees cooler than the heatwave in parts of Spain and Portugal, where the mercury was set to soar past 40C.
But Met Office deputy chief meteorologist Rebekah Sherwin said the UK highs would continue into early next week.
"From Sunday and into Monday, temperatures are likely to be in excess of 35C in the southeast (of England), although the details still remain uncertain," she said.
"Elsewhere, temperatures could be fairly widely above 32C in England and Wales, and in the mid-to-high 20s Celsius further north."
Britain's highest recorded temperature was 38.7C at Cambridge Botanic Garden, in eastern England, on July 25, 2019.
Sherwin said meteorologists could not rule out that record being broken but it was "still only a low probability".
"A number of weather scenarios are still possible and at the current time, mid- or perhaps high-30s are looking more likely," she added.
The extreme heat warning was classified as "amber", the second-highest of three, indicating a "high impact" on daily life and people.
Mark McCarthy, head of the Met Office National Climate Information Centre, said "strongly embedded warming due to climate change" across Europe was increasing the chances of a new UK record.