Millions more Britons have been advised to brace themselves for a cold snap after forecasters issued fresh ice warnings on Monday.

The Met Office issued a yellow warning for ice across southern England and South Wales, which will last from 3pm on Monday to 3am on Tuesday.

The wintry weather comes after Prime Minister Rishi Sunak visited flood-hit residents in Oxford, and Environment Agency (EA) workers are still trying to mop up from the heavy rainfall and high winds during Storm Henk last week.

People in London and the South East woke up to ice, sleet and snow showers on Monday morning.

Temperatures dipped to -8C at Altnaharra in the Scottish Highlands and temperatures are expected to be lower than average for this time of year for much of the week.

Southern parts of the UK are set for “ice and small amounts of snow” which could cause icy patches on some roads and lead people to fall on slippery surfaces.

Meanwhile, the EA said “significant” floods are expected to continue on parts of the lower River Trent on Monday with minor impacts expected there and along the rivers Thames and Severn until Wednesday.

Minor groundwater flooding is expected across parts of Dorset, Wiltshire and Hampshire and could possibly hit other parts of the south as well as Yorkshire.

Met Office spokesperson Stephen Dixon said the sudden change in conditions is due to cold air from the north and east replacing wet westerly air.

He added that clear conditions and some sunny spells are expected, while 1-2cm of snow could fall on some higher ground such as Dartmoor.

He went on: “It is a cold regime and that theme continues for much of the week

“Temperatures through the week will remain below average for this time of year.

“If you do have to travel in icy conditions plan your route, check for delays and road closures.

“If you are driving … look out for potential hazards and keep your speed down. Using a higher gear may be more appropriate.”

Tuesday night could be even colder with temperatures potentially dropping to -9C in the Scottish Highlands, while daytime temperatures are not expected to top 6C in the south and 8C in the north.

An amber cold health alert (CHA) for the North West of England, the Midlands, the South West of England and the South East of England is also in place until noon on Friday.

The amber alert, issued by the UK Health Security Agency (UKHSA), means “cold weather impacts are likely to be felt across the whole health service for an extended period of time”.

There is also a yellow cold health alert in place for the North East of England, Yorkshire and the Humber, the East of England and London.

Cold weather can raise the risk of heart attacks, strokes and chest infections, and is particularly dangerous for the elderly and people with underlying health conditions.

Dr Agostinho Sousa, head of extreme events and health protection at UKHSA, said: “With the Met Office forecasting drops in temperature across the United Kingdom into next week, it is important to check in on the wellbeing of those most vulnerable to the cold.”

The Environment Agency said around 2,000 properties have flooded.

On Monday afternoon, there were 139 flood warnings in place, where flooding is expected, and 144 flood alerts for southern parts of England, up through the Midlands and into Yorkshire.

Mr Sunak sought to defend the Government’s record on flood protection as he spoke to the media in front of the fast-moving River Thames on Sunday.

He said: “We have over 1,000 Environment Agency personnel on the ground in local communities helping, over 200 pumps have been deployed.

“We’ve invested £5.2 billion in flood defences over the period in question – that’s a record sum, far more than we’ve done (previously); in the future that’s contributed to protecting over 300,000 homes.

“And, of course, there have been many people affected by what’s happened over the past week, but also over 49,000 have been protected from flooding.”

Labour leader Sir Keir Starmer said the Government’s record on flood defences is “not good enough” as he toured streets being cleared up after last week’s deluge.

During a visit to Loughborough, Leicestershire, the opposition leader said he would set up a flood resilience task force to make sure preventative measures were in place before the winter flooding season.

He added: “The response wasn’t quick enough. So I just don’t think it’s good enough for the Government to come after the event again and express empathy.

“Get ahead of this with a taskforce. That’s what I would do.”

Asked if Labour would provide more money for flood prevention, Sir Keir said: “Of course it does need money but the taskforce is not just about money.

“It’s about getting the basics done. Getting those drains cleared. Getting the local authorities together. Having a plan.”