Councils and emergency services have been warned to be prepared for temperatures of up to 30C (86F) to last until October.
In the longer term, the Met Office's analysis has suggested hot, dry conditions could return and continue into the autumn.
The forecast says this year is twice as likely than usual to have the hottest August to October period recorded in the United Kingdom since before 1981.
"This also increases the chances of above-average United Kingdom temperatures, particularly in the early part of the forecast period".
Ms Diamond said: "This means there is an increased likelihood of warmer-than-average temperatures and below-average rainfall".More news: New Barca signing Vidal determined to win three Champions Leagues
The three-month outlook suggests a greater likelihood of high-pressure systems near the United Kingdom, meaning settled conditions are more likely than unsettled weather.
"Further, warmer-than-average temperatures does not necessarily mean sunshine - it can be warm and cloudy too".
The Met Office said the mercury could reach 34C in Essex, Norfolk, on Tuesday as warm air from the continent continues to swelter the UK.
"A fresher night where it has been so muggy and we will see temperatures fall to 15C, and Scotland and Northern Ireland in rural areas are down into single figures".
However, maximum temperatures are likely to dip to around the mid-20Cs mark come Wednesday.More news: Vote by smartphone? This state is introducing it
Nicola Maxey, spokesman for the Met Office, said: "We are looking at a cooler spell as we go through the next few days".
Whilst the intense heat of the previous weeks does look to have passed, warm weather is expected to remain in the United Kingdom until October, because of a global heatwave that has seen record temperatures set across Europe.
British holidaymakers are being warned to avoid spending time in the sun during the hottest part of the day and to keep hydrated.
Red health alerts for extreme heat have been issued for more than half the country and hot, dry conditions have led to several wildfires.
The Met Office has issued another yellow thunderstorm warning.More news: What did we learn about Josh Gordon from Hard Knocks?
Authorities said the conditions played a part in the deaths of two men, one in Barcelona and the other in the southern Spanish region of Murcia.