Torrential downpours will soak Britain this week as a month’s rainfall causes possible flooding, forecasters have warned.
Up to 5cm of rain is expected to fall on Thursday and Friday, interrupting the summer holidays for millions of families.
Motorists were warned about dangerous flash floods as severe weather warnings were issued for most parts of England and Wales.
But the Met Office insisted that summer was not yet over, with periods of much drier, warmer weather forecast for much of the end of August and beginning of September.
Helen Roberts, a spokeswoman, said that warm air moving in from the south on Thursday would make it feel very humid across central and southern areas of the UK.
“Thundery conditions will start pushing up from northern France from about midnight on Wednesday,” she said.
“They will gradually move northwards through the early hours bringing some very heavy downpours and nasty rush-hour conditions.
“The heaviest rain will be across southern and central regions and we are not ruling out seeing a months worth of rain over the warning period.
“It is also going top feel very muggy through Friday and with any cloud breaks temperatures could really shoot up, we could see 27C (81F).
“Thermometers in the south will dip to a less muggy 20C (68F) by the weekend with a much fresher, calmer outlook for the whole country.”
Total rainfall across England and Wales is expected to be between 30 and 50mm from Thursday to Friday, which is the average total for the whole of August.
The weather system is expected to clear away to the east during Saturday, with drier, fresher weather following everywhere, with some sunshine.
Paul Watters, head of roads policy at the AA, offered advice to motorists who may get stuck in floodwater.
He said: “Flash-flooding in the summer can be hit-and-miss but potentially dangerous for anyone caught up in it. The AA advises drivers to keep an ear out for local weather warnings and traffic news, and be prepared to encounter flooding.
“Flooding close to where you live may present less of a problem as most drivers know which are the hazardous stretches of road and can avoid them. Those on holiday face a more precarious challenge and asking local people where they might run into flooding is a wise move.”
The AA said motorists should only drive through water if they know it is not too deep – generally no more than halfway up the wheels. They should also not try driving through fast-moving water, such as in a ford, as the car could easily be swept away.
Drivers are advised to stay in their car and telephone for help if trapped in water or wait for the flood to subside.
Despite the dismal outlook, forecasters insisted that summer temperatures would return, with much of the rest of August and September likely to be warm and bright.
Helen Roberts, a Met Office forecaster, said: “There will certainly be further warm spells.
“Towards the end of next week, while there will be more unsettled conditions in the north west, it should be much drier and brighter in the south east.
“As we look towards the end of August and into September, areas of high pressure will start to build which will lead to more settled conditions.
“In the south, pasrticularly, temperatures will be close to average for this time of year, if not a little higher.”