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.
As at 7.30am there were 78 flood warnings and 191 flood alerts across the nation.
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 on Tuesday meant “we could see as much as 40 to 50mm maybe in a couple of hours in some spots”.
The Met Office has issued a yellow weather warning for Wales, southern England, East Anglia and the Midlands between 6am and 8pm on Tuesday.
It warns of heavy showers and disruption caused by flooding.
A yellow warning of heavy rain is also in place for southwest Scotland until 10am.
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 due at 8.40am on Tuesday and predicted force six north-westerly winds could result in flooding in the west Norfolk area.
People are 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”.