Met Office meteorologists said temperatures are forecast to rise day by day, and could reach 30C in London by Wednesday.
The current record for this year was set on May 20, when the mercury reached 28.2C at Santon Downham in Suffolk.
This beat the previous record set just the day before when London’s St James’s Park recorded a high of 26.2C.
Saturday, when this year’s summer solstice will occur, is due to be mainly sunny and fairly warm, but rain showers will cover most of the country through the night.
Meteorologist Emma Salter said the whole country will experience wet and windy weather overnight, although rain is unlikely to last more than a few hours.
This is good news for regions like Derbyshire, which saw flash flooding after stormy weather hit this week.
Sunday will also be warm and sunny, though there is a divide between the south-east of the country where clear skies are expected, versus north-west Scotland and Northern Ireland where cloudy weather is due.
Ms Salter said: “England and Wales should be totally clear of cloud from Sunday, with temperatures building day on day.
“Scotland and Ireland could be more cloudy and overcast, but temperatures will still be warmer.
“Wednesday could be the hottest day of the year so far, with temperatures expected to reach 30C in London.”