Sites based on user-generated content (UGC) are seeing huge gains usage in the UK, according to data recently released by comScore Media Metrix.

In July, the five UGC sites that ranked in the top 50 sites in the UK (measured by total visitors that month)— Wikipedia, MySpace, Piczo, YouTube and Bebo — generated an average of 4.2 usage days and 79.9 minutes per visitor, according to comScore. By comparison, sites in the top 50 that were not based on UGC saw far less usage. Visitors went to these sites an average of 3.5 days and spent an average of 33 minutes.

Even more compelling were the page view statistics that comScore released. Visitors to UGC sites viewed an average of 217 pages, compared with 52 at non-UGC sites. Bebo visitors viewed an average of 428 pages during the month, while MySpace visitors viewed 333.

These UGC sites have also experienced significant traffic growth over the past year. MySpace was up by 467%, to 5.2 million unique visitors in the UK in July, while Piczo rose by 393%, to four million.

"Many of the sites experiencing the fastest growth today are the ones that understand their audience’s need for expression and have made it easy for them to share pictures, upload music and video, and provide their own commentary, thus stimulating others to do the same," said Bob Ivins, managing director of comScore Europe.

However, without seeing actual usage statistics for other sites in the UK top 50, it is difficult to know exactly how dominant the UGC sites really are in the UK. In similar usage statistics released by comScore for the US market, for example, several non-UGC site families generated more usage days than MySpace or Facebook. Yahoo! sites and the Time Warner Network generated 11.6 and 10.4 average usage days per visitor, respectively, followed by Microsoft sites and the Weatherbug property. MySpace was fifth, with 8.7 usage days.