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The Met Office has warned torrential downpours and thunderstorms could bring flooding and travel disruption to much of England and Wales this week.
Forecasters have issued yellow severe weather warnings for thunderstorms across large swathes of the UK on Tuesday and Wednesday.
The heavy rain will bring a risk of flooding to some homes and businesses, along with road closures and cancellations of train and bus services.
"Heavy showers and thunderstorms will continue to spread north-east across England and Wales, while also increasing in frequency during the day,” Met Office forecasters warned.
"In a few places there is the potential for 20mm to 30mm of rain to fall in an hour and 30mm to 50mm of rain to fall in three hours.”
UK heatwave rolls in as temperatures soarShow all 44 1 /44UK heatwave rolls in as temperatures soar UK heatwave rolls in as temperatures soar Bournemouth Hundreds of people at the beach in Bournemouth, as the UK could encounter the hottest July day on record
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UK heatwave rolls in as temperatures soar Manchester Hamza and Haris splash in the water feature beside the National Football Museum
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UK heatwave rolls in as temperatures soar Derbyshire People play in the water at Hathersage Outdoor Swimming Pool
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UK heatwave rolls in as temperatures soar Whitley Bay Sunrise at St Mary's Lighthouse
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UK heatwave rolls in as temperatures soar Margate Families fish for crabs from a sea wall
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UK heatwave rolls in as temperatures soar Surrey People leap from a bridge at Taggs Island, near Hampton Court
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UK heatwave rolls in as temperatures soar London Ireland's players in a drinks break during the second day of the test match against England at Lord's
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UK heatwave rolls in as temperatures soar London People sunbathe in Hyde Park
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UK heatwave rolls in as temperatures soar Manchester People splash in the fountains in Piccadilly Gardens
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UK heatwave rolls in as temperatures soar Margate Families make their way to the beach
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UK heatwave rolls in as temperatures soar Cambridge People use umbrellas to shield from the sun as they punt along on the River Cam
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UK heatwave rolls in as temperatures soar Brighton People enjoy the hot weather on the beach
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UK heatwave rolls in as temperatures soar London England's Jack Leach cools down with a towel in a drinks break
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UK heatwave rolls in as temperatures soar Margate
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UK heatwave rolls in as temperatures soar Northumberland Kadie Lane, 10, cools off in the fountain at Alnwick Gardens. The UK is bracing itself for what could be its hottest ever day after lightning storms triggered fires and rail disruption
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UK heatwave rolls in as temperatures soar Hampshire Lightening striking as a thunder storm passes over Basingstoke
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UK heatwave rolls in as temperatures soar Northumberland Visitors sit in deckchairs in the sun at Alnwick Gardens
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UK heatwave rolls in as temperatures soar West Yorkshire Sisters, Nyam May (left) and Ciara May (right), jump into the water at Ilkley outdoor pool and lido
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UK heatwave rolls in as temperatures soar An African white lion sunbathes at West Midlands Safari Park
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UK heatwave rolls in as temperatures soar Liverpool Lightening strikes as a thunder storm passes over houses in Lee Park
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UK heatwave rolls in as temperatures soar Northumberland Children sit in the sun by 'The Friendly Giant', a pond sculpture situated in Alnwick Gardens
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UK heatwave rolls in as temperatures soar Northumberland Reuben Humphreys, 4 , cools off in the fountain at Alnwick Gardens
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UK heatwave rolls in as temperatures soar West Yorkshire
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UK heatwave rolls in as temperatures soar Pembrokeshire Holidaymakers shelter under umbrellas on the South Beach,Tenby
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UK heatwave rolls in as temperatures soar Lincolnshire A thunder storm passes over Holbeach St Marks
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UK heatwave rolls in as temperatures soar Pembrokeshire Swimmers have fun in the sea on a giant inflatable Flamingo, South Beach
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UK heatwave rolls in as temperatures soar Folkestone Sunbathers relax
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UK heatwave rolls in as temperatures soar West Yorkshire
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UK heatwave rolls in as temperatures soar Kent Broadstairs beach
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UK heatwave rolls in as temperatures soar Pembrokeshire South Beach,Tenby
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UK heatwave rolls in as temperatures soar Dog owners warned about heatstroke American Bulldog Finlay, receiving urgent cooling treatment at PDSA's Pet Hospital, after was left fighting for his life after his body temperature soared to a life-threatening 42.2C (108F) during recent hot weather
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UK heatwave rolls in as temperatures soar Folkestone A couple, seen through heat haze
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UK heatwave rolls in as temperatures soar Ilkley Freddie Ward jumps into the water at Ilkley outdoor pool and lido in West Yorkshire as the UK is expected to edge towards its hottest ever July day
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UK heatwave rolls in as temperatures soar Pembrokeshire North Beach,Tenby
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UK heatwave rolls in as temperatures soar Pembrokeshire
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UK heatwave rolls in as temperatures soar Canterbury People enjoy punting through Westgate Gardens as temperatures rise across the UK this week
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UK heatwave rolls in as temperatures soar Pembrokeshire
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UK heatwave rolls in as temperatures soar Ilkley People play in the water at Ilkley outdoor pool and lido
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UK heatwave rolls in as temperatures soar Canterbury Isla Stanton enjoys the sunshine in Westgate Gardens
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UK heatwave rolls in as temperatures soar Pembrokeshire
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UK heatwave rolls in as temperatures soar Oxford
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UK heatwave rolls in as temperatures soar Pembrokeshire
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UK heatwave rolls in as temperatures soar Warwickshire People enjoy a trip in a boat along the river in Stratford Upon Avon
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UK heatwave rolls in as temperatures soar Stratford Upon Avon
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The UK usually sees about 78.1mm of rainfall in July on average, according to data collected by the Met Office between 1981 and 2010.
Hail is also possible in northern England and yellow weather warnings come with a "small chance of fast flowing or deep floodwater causing danger to life", the forecaster said.
The first warning, which will run until midnight on Tuesday, will cover almost all of England and Wales, excluding East Anglia and the southeast.
A second weather warning for thunderstorms on Wednesday will cover parts of Scotland, North Wales, north England and the Midlands.
The risk of sudden flooding will be a shock for many people after the record-breaking heatwave that swept across the country last week.
On Thursday, the UK saw its hottest day ever when a temperature of 38.7C was recorded at Cambridge Botanic Garden, beating the previous record of 38.5C set during a heatwave in 2003.
However, Marco Petagna, a Met Office meteorologist, said that the unsettled weather is not unusual for this time of year, although it will be a sharp contrast to recent weeks.
He added that the worst conditions are expected to pass after Wednesday.
“The trend through the week is for things to become less intense, but there are signs of some more unsettled weather coming in at the weekend,” Mr Petagna said.
Agencies contributed to this report
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