Britain's heatwave has sent ice cream sales soaring - and the warm weather is set to last with the country predicted to be hotter than Ibiza, Athens and Barcelona tomorrow. Some ice cream vendors say they have had their busiest April ever as Britons cool off, with the balmy conditions set to continue. The mercury is predicted to soar to 21C (70F) tomorrow, with forecasters warning people to make the most of it before the weather turns for the worse in the second half of this week. Scroll down for video . Beach bums: Two sunbathers take advantage of the hot weather as they bask in the sunshine in Old Portsmouth, Hampshire . Summertime already: Two friends settle down for an al fresco lunch on Bristol's College Green as they enjoy the warm weather . Britain's heatwave has sent ice cream sales soaring, with Lily and Jack Manning, aged 11 and six, enjoying the treat in Old Portsmouth this afternoon . A gaggle of greylag goslings take in the sunshine on the banks of the river in Sonning-on-Thames in Berkshire . Hot dog: A woman and her canine companion enjoy a stroll in Green Park, London, where temperatures could hit 21C tomorrow . Ice cream vendor Katy Alston, 47, known as Mrs Whippy to her customers in the Sussex towns of Bognor Regis and Chichester, said the good weather has sent ice cream sales through the roof. She said: 'We have had a nice warm April and it has been absolutely amazing for sales. 'In April we usually potter around and find our feet, but this year it has been really busy. We did an event last week at Chichester University and sold out of ice creams in 40 minutes. It was just incredible - and it's down to the weather. 'Everybody says people eat ice cream all year round whatever the weather, but they don't. Children want to but adults won't let them. 'We have had our best April ever and I have been in business for 11 years. I would say our turnover for April has trebled.' Ms Alston, who runs the business with her daughter Georgia, 23, who is known as Little Miss Whippy, said the traditional 99s, and lemonade and cherry brandy ice lollies are her biggest sellers. The Met Office said most of Britain, including these three young women in Green Park, basked in sunshine today and will continue to enjoy good weather until Wednesday . Some ice cream vendors say they have had their busiest April ever as Britons cool off, including two-year-old Fernella, who looked to be enjoying her cold Smarties treat in Cannon Hill Park in Birmingham . Hot trot: Two ducks appear to be leading three horses for a stroll through London's Green Park - but rain is forecast for the capital this weekend . Basking in the sunshine: A group of people line up beneath the historic hot walls in Old Portsmouth, with one man dipping his toes in the water . Beautiful day for a stroll: A couple walk hand in hand along the towpath by the Kennet and Avon Canal in Berkshire today . Enjoy it while you can: Two women tuck into strawberries in front of the Royal Crescent in Bath, but cooler conditions are expected from Thursday . A spokesman for the Ice Cream Alliance, which represents UK sellers, said: 'The hot weather has given ice cream sales a terrific start to the summer season. 'Some of our members have reported an increase in sales of ice creams and lollies of 400 per cent, all due to the sunny weather.' But the industry could take a hit later this week, with rain, cloud and cooler temperatures predicted from Thursday. Forecasters said showers could hit London this Sunday as tens of thousands of runners take part in the London Marathon. Dan Williams, a spokesman for the Met Office, said most of Britain has basked in sunshine today and will continue to enjoy good weather until Wednesday. He said: 'There has been lots of sunshine around and the temperatures have been pretty decent for this time of year - temperatures have hit 19C in Sussex and 18C in London. 'Generally speaking most places have had some decent sunshine. 'Tomorrow is a good day again in England and Wales, lots of blue skies and sunshine and temperatures in the high teens.' One man took his shirt off to catch some pre-summer rays in a park in London, but rain could hit the capital for Sunday's marathon . Sunbathers were out en masse in the beach in Old Portsmouth, Hampshire, were the sun is expected to last tomorrow and on Wednesday . Caught napping: Taylor Messenger was rudely awoken by friends Gabrielle Thompson and Harriet Crosby, who threw a bucket of cold sea water over him as he slept on the beach at Scarborough . A pair of mothers chat as they push their children through Cannon Hill Park in Birmingham, where flowers are well and truly in bloom . A couple enjoy their lunch in the shadow of the Clifton Suspension Bridge in Bristol as the UK continues to bathe in sunny weather . Kendal, in Cumbria, was treated to a glorious golden glow this morning as dawn broke across the rolling fields outside the market town . It was a less pleasant start to the day for this rower, who was out in fog on the river Cam in Cambridge in the early hours of this morning . Mr Williams added: 'By Thursday a lot more cloud will be around in general and there will be light rain over Scotland. 'For most it will be a dry day still with some sunny spells, but generally that cloud is the herald of slightly more unsettled weather. 'The high pressure that has been dominating for the past few days moves over and we see a bit more of what you would expect this time of year.' Patchy rain and breezier conditions are expected to hit at the weekend, and could bring unsettled conditions as runners line up for the London Marathon.
Britain's heatwave sends ice creams sales soaring - with some vendors seeing a 400 per cent rise in sales .
Temperatures forecast to hit 21C tomorrow, with the country set to be warmer than Ibiza, Athens and Barcelona .
But the balmy conditions could be coming to an end, with clouds, wind and a spot of rain forecast for Thursday .
Showers predicted to hit London on Sunday as tens of thousands of runners take part in the London Marathon .