The rain warning comes after another weekend of wildfires across London, including in Enfield, Rammey Marsh and Turkey Street.
Hundreds of firefighters worked to douse flames that threatened a school, nearby roads and animals.
The grass fires were some of the hundreds that London Fire Brigade (LFB) has responded to in the first two weeks of August, while on Friday around 50 firefighters were called to a blaze which scorched two hectares of grass in Leyton Flats park near Whipps Cross Road.
Such has been the extent of the dry conditions that the LFB has responded to eight times as many grass and open land fires in the first week of August compared with the same week last year.
Fire crews were also called to fires in Canvey Island and Harlow, Essex, while in Kent, firefighters spent Saturday dousing flames which had ripped through ten hectares of land on Dartford Heath.
Other wildfires were reported in Lincolnshire, West Midlands, Wiltshire and Dorset, where emergency crews reported an increase of 492 per cent in the number of incidents in August compared with same period in 2021.
The fire in fields surrounding a school in #Enfield is now under control. The blaze spread to a field with two horses who were moved to safety. Thankfully no buildings were affected. https://t.co/lkYm95zSsP pic.twitter.com/do7gbiMMlo
— London Fire Brigade (@LondonFire) August 14, 2022
Meanwhile runners struggled in the heat, with four being taken to hospital after collapsing during a half marathon event in Richmond Park on Sunday.
A search is continuing for a swimmer who got into difficulty in the Thames near Hampton Court bridge on Sunday afternoon.
The Met Office has issued a thunderstorm warning from 10am on Monday.
“Hit-and-miss thunderstorms likely to develop through Monday, producing some torrential downpours for some spots, and possible disruption,” it warned.
Britons can expect sudden flooding which could cause road closures, travel delays, and possibly power cuts.
“There is a small chance that homes and businesses could be flooded quickly, with damage to some buildings from floodwater, lightning strikes, hail or strong winds,” the Met Office said.
Temperatures are forecast to drop to 28C on Monday in London, 25C on Tuesday and 23C on Wednesday.
England needs “weeks of rain” to stop the drought which is impacting multiple parts of the country experts have warned.
Eight areas in the UK have been placed in drought conditions: Devon and Cornwall, Solent and South Downs, Kent and south London, Hertfordshire and north London, East Anglia, Thames, Lincolnshire and Northamptonshire, and the east Midlands.