The UK unique users grew from 17,000 in June 2007 to 444,000 in June this year, which was an increase of 2,575%.
, the classifieds site for jobs, cars and homes was the second fastest growing website. Its UK users jumped from 30,000 in June last year to 766,000 in June this year.
Shopping comparison site was placed third with a growth of 1,443%.
Two other reward sites also made it into the top 10 fastest growing UK websites. These were , which was placed fourth with a growth of 1,200% and , which was placed seventh after increasing its UK users by 828%.
Alex Burmaster, internet analyst for , said: "Sites tapping into consumer concerns about the economy, giving them the opportunity to save money, dominate the fastest growing list.
"Coupons and reward sites, classifieds and shopping comparison engines are obvious examples but Walkers Snack Foods is the fastest growing site of all due to their 'Brit Trips' promotion offering discounts on British holidays and trips around attractions, hotels and restaurants."
was the fastest-growing website (57%) among the 10 most popular UK sites, followed by (52%) and (41%).
Microsoft's , which is the ninth most popular UK website, lost 7% of its UK audience over the past year, while Microsoft's Windows Media Player dropped by 3%.
Burmaster said: "[Microsoft's] Windows Media Player and Hotmail properties have been casualties of the social media explosion -- consumers streaming video directly on sites instead of using media players and increasingly communicating via Facebook rather than email.
"[Its] messenger service has a smaller footprint -- reaching less of the overall internet population -- than it did a year ago, despite a slight upturn in audience."