The weather will remain unseasonably warm over the next few days before temperatures drop later in the week, the Met Office has said.
Grahame Madge, a spokesperson for the Met Office, said: “There is potential for 21C – possibly in London or somewhere in the south-east – today.”
“And tomorrow we might see an isolated 23C, which is obviously a lot higher than we would expect at this time of year,” he added.
Elsewhere, parts of north and west Scotland may experience rain on Tuesday.
Later in the week, temperatures will drop and there will be a greater chance of rain.
Mr Madge said the weather will change from Thursday, becoming “more unsettled” over the weekend and bringing the prospect of more showers.
Temperatures will also plunge to nearer the monthly average. In England, the average temperature for April stands at around 12.5C.
The good forecast for the middle of the week follows a period of sunny weather last weekend, when officials urged members of the public not to break the government’s restrictions.
Photos emerged over the weekend showing police officers ordering sunbathers, who were in breach of the lockdown measures, to leave parks.