Social networking sites are on the rise in the UK and ad spending on such sites is expected to reach £285 million ($533 million) by 2012, according to eMarketer's recently released "UK Social Network Marketing: Ad Spending and Usage" report - MarketingCharts writes.

Some 11 million people, or 30 percent of UK internet users, spent time at sites like Bebo, MySpace and Facebook, eMarketer estimates. Those three sites account for the lion's share of users in the UK.

Though social sites account for only a tiny portion of UK online ad spending (3.4 percent in 2008), social-network ad spend will rise 77 percent this year to £115 million ($225 million), eMarketer projects. Spending in 2012 will have increased 148 percent over 2008 levels

Social networks have been part of the UK internet landscape for several years, and the UK dominates social-network spending in Western Europe with 68 percent of the market.

eMarketer expects the UK social-network market to enjoy slightly greater ad-spending percentage gains than that of the US; the UK social-network ad market trails that of the US by one to two years.

"Though social network advertising is forecast to grow aggressively this year, it will only do so if social network operators can develop substantial metrics showing the value and performance of the advertising," said Debra Aho Williamson, author of the report.