The heatwave is set to continue well into next week in parts of Britain, following a weekend of record-breaking temperatures.
The mercury peaked at 30C (86F) in parts of the country yesterday, making it not only the hottest day recorded in October, but the third hottest of 2011.
And the unseasonably warm weather will carry on until Tuesday in the South East, forecasters said, when the highest temperature will be a cooler 20C (68F).
Gareth Harvey, forecaster at MeteoGroup, the weather division of the Press Association, said: "It will be fairly miserable across northern Ireland Scotland today, with further spells of rain, but the fine weather should hold up in parts of England and Wales.
"It might be more unsettled across northern Wales and northern England, but for most of central, south-eastern and southern parts of England it should be another nice day.
"It might not be as warm as yesterday, but we'll see the odd 29C (84.2F) in one or two spots towards the South East.
"It cools down a bit on Monday, but temperatures will be still be well above average - around 25C (77F) in the South East and East Anglia."
The weather will be fresher on Tuesday, however, with highs of around 20C (68F) in the South East.
"This is still above average, but not well above average," Mr Harvey said.
Similar temperatures are expected on Wednesday, but cooler air will set in on Thursday.
Mr Harvey said: "From Thursday onwards it will be very windy, with some cool air across the whole of the country and some heavy showers.
"Temperatures on Thursday will peak to 17C (62.6F) or 18C (64.4F) in the South East. By Friday the highest temperature in the country will be about 15C (59F) or 16C (60.8F), which is half of what we saw yesterday."
Yesterday's scorching weather saw the UK top temperatures in the holiday hotspot islands of Ibiza and Majorca and the Spanish capital Madrid.
But not everybody in Britain shared in the heatwave. While people in much of the country headed for beaches and parks to soak up the sunshine or fired up barbecues, rain fell on parts of Scotland and Northern Ireland.
RAF Finningley in Yorkshire recorded a sweltering 30C (86F) at 3pm, MeteoGroup said.
Gravesend in Kent was not far behind - reaching 29.6C (85.3F) at 3pm.
The previous October record of 29.4C (85F) was set in March, Cambridgeshire in 1985.
Wales also broke its October record, which had stood since 1985, when Hawarden reached 28.2C (80.6F) shortly after 2pm today.
The UK's hottest day of 2011 was June 27 when a temperature of 33.3C (91.9F) was recorded at the Olympic Park in London. The previous day, St Helier on the island of Jersey reached 30.8C (87.4F) - leaving today's high of 30C in third place.
The UK pipped Madrid at 26C (78.8F) as well as Ibiza and Majorca which were both reading 27C (80.6F) at 3pm.
Traffic was heavy across England as sunseekers packed their buckets and spades and headed towards holiday hot-spots.
Trafficlink communications manager Andrea Day said roads in the north were very busy, particularly the A64 between Yorkshire and Scarborough and the M55 heading towards Blackpool.
"Normally we would see this kind of traffic on a bank holiday weekend or a sunny weekend during the summer, so to see it at this time of year is really quite unusual," she said.
One of the longest queues was heading towards the seaside resort of Southend, Essex, with vehicles stretching for 15 miles.
Miss Day warned motorists to check traffic reports before heading out on the road. This afternoon between 3pm and 8pm is likely to be particularly busy as weekend trippers make their way home.
Sunbathers packed the beaches in Brighton, which has seen a massive rise in visitor numbers this week.
Officials reported a 30% increase in people clicking on to the city's official tourist website, visitbrighton, and calls to the Brighton visitor information centre rose by more than 50%.
Tourism councillor Geoffrey Bowden said the boost in visitors was a "welcome fillip" at the end of the summer season and helps support the 13,500 jobs dependent on tourism in Brighton.
He said: "Brighton and Hove always looks brilliant in the sunshine and it's no surprise that visitors are heading our way to make the most of it."
The warm weather was also helping events such as Brighton Oktoberfest as part of the five week-long Brighton and Hove Food and Drink Festival.
The event's managing director Nick Mosley said Friday night was sold out and last night would be too, adding: "The good weather always helps."
Meanwhile, confused plants are flowering again due to the unseasonably warm weather, according to experts.
The Royal Horticultural Society (RHS) said strawberries and rhododendrons were among the plants seen blooming at its flagship garden in Surrey when they were not expected to flower again until next spring.