The Met Office has warned of torrential rain and thunder in parts of the country on Tuesday.
Some regions are expected to receive the equivalent of two weeks worth of rain in less than an hour.
At 10:30am on Tuesday, there were 70 flood warnings and 184 flood alerts in force.
On the Isle of Man, an island off the north-west coast of England, police declared a “major incident” after severe flooding swept away several vehicles and left people trapped in at least three homes.
Residents on one flooded road in Laxey, a village on the east coast, were told to wait upstairs in their homes after it was deemed they were safer inside their homes.
Power was shut off in 150 homes for safety reasons, but has since been restored, police said.
In the UK, yellow weather warnings remained in place across much of southern England, the Midlands and Wales.
Speaking on Tuesday morning, Met Office meteorologist Luke Miall said: “We could see some local quite torrential downpours and a risk of surface water flooding.”
He warned that slow-moving clouds meant “we could see as much as 40 to 50mm maybe in a couple of hours in some spots”.
Derbyshire Fire and Rescue Service said officers rescued an adult and a child trapped in a vehicle caught in floodwater in Bretby, near Burton upon Trent, at around 8pm on Monday.
At around 9pm, crews from North Yorkshire Fire and Rescue Service went to the aid of a woman in a car stuck in floodwater in Cattal Moor Lane, near York.
Photographs taken at the Ship Inn pub in Mevagissey, Cornwall, on Monday night show floodwater inside the pub and nearby roads submerged.
In west Norfolk, a “precautionary evacuation notice” has been issued for the coastal areas of Hunstanton, Heacham and Snettisham.
The Environment Agency said a combination of a high tide at 8:40am on Tuesday and predicted force six north-westerly winds could result in flooding in the west Norfolk area.
People were being told to leave caravans and properties in the affected area between 7am and 10am on Tuesday and not to return until it is safe to do so.
They have been urged to take with them any medication, pets and anything urgent they might need over the next 48 hours.
The public are also being advised to take care along beaches, promenades, coastal footpaths and roads as large waves and sea spray could be dangerous.
In the South West, the Environment Agency told people to avoid the seafront and check flood warnings due to forecast high tides and winds.
On Tuesday it said predicted heavy showers could bring a “small chance of fast-flowing or deep floodwater causing danger to life”.