According to Nielsen Online, last month the average Briton spent 22 hours 20 minutes online or using internet-related applications, which represented a 34% increase on a year ago when the figure was 16 hours 36 minutes.
Facebook is one of the major factors in increasing the time that people are spending online. The amount of UK time spent on the social networking site increased from 2.4bn minutes in April 2008 to 6.2bn minutes in April 2009, or 12.7% of all UK internet-related time.
The second most heavily-used web brand during the month was MSN/Windows Live, which includes the Messenger and Hotmail services. UK users spent 4.46bn minutes with the brand or 9.2% of total internet time.
Google came in third, with users spending 2.56bn minutes on the site during April 2009 or 5.3% of their total internet time.
Alex Burmaster, communications director, EMEA, at Nielsen Online, said: "The Internet is a complex and varied ecosystem and I think most people would be surprised by just how much time is accounted for by a relatively few brands who, in turn, are increasing their share of the pie.
"Between just the two of them, the two most heavily used web brands -- Facebook and MSN/Windows Live -- account for almost 11bn of the 48bn minutes that Britons spend online.
"That's over one in every five minutes and highlights just how competitive the online space is for both publishers and advertisers when it comes to capturing consumer attention."
Communication and entertainment are the two central themes among the most heavily-used web brands.
Yahoo! and AOL also scored heavily on time due to their email offerings, as did video-sharing site YouTube and the technology companies Microsoft and Apple, due to their media player offerings -- Windows Media Player and iTunes.
Burmaster said: "The major players have had a pretty good year in terms of the increasing amount of time people spend on their websites and applications.
"This bodes well for the online industry as it attempts to attract the big brand advertisers by providing a more meaningful platform to engage consumers, particularly through the vehicles of entertainment and communication."
Nielsen Online: Most heavily-used web brands -- share of UK Internet-related time
Rank, Brand, Share of time April 09, Share of time April 08, Change in share of time.
- Facebook, 12.7%, 7.2%, +5.6%
- MSN/Windows Live, 9.2%, 10.1%, -0.9%
- Google, 5.3%, 4.8%, +0.4%
- eBay, 4.1%, 5.0%, -0.9%
- Yahoo!, 3.5%, 4%, +0.1%
- AOL Media Network, 3.0%, 3.2%, -0.2%
- BBC, 2.3%, 2.3%, +0.1%
- YouTube, 1.9%, 1.9%, -0.1%
- Microsoft, 1.5%, 2.0%, -0.5%
- Apple, 1.5%, 1.7%, -0.2%
Total 45.1%, 41.6%, -