In May the social network attracted 26.8 million visitors, which is seven percent up on the same period last year. As a result, Facebook surged past Microsoft's MSN/WindowsLive/Bing sites, which had previously been in second place, with 26.2 million combined visits. However, it still has some way to go to topple Google, which had 33.9 million visitors in the same month.
Furthermore, the number of Facebook members grew by 41 percent between 2009 and 2011, with the over-50s making up the majority of new members.
"The growth in audiences to these social networks is now primarily being driven by the 50-plus age group. Just a few years ago, this group may have found itself out of place on these sites," UKOM general manager James Smythe said.
Twiter's user base showed a similar pattern, with visitors jumping to 6.1 million after the micro-blogging site was used to name Ryan Giggs as the premiership footballer behind a super injunction that stopped the media publishing details of an alleged affair with Big Brother star Imogen Thomas.
According to UKOM/Nielsen, the number of women over 50s on the site doubled after 'Giggsgate'. However, under-18s appears to have lost enthusiasm for Twitter and are less likely to visit the micro-blogging site.
LinkedIn had3.6 million UK visitors in May, which is a 57 percent increase on the previous year.