Litigation heavyweights Carter Ruck and Herbert Smith are crossing swords this week as one of the most high-profile libel cases to reach the High Court for years gets underway.

The case sees Carter Ruck represent the founder of advertising and marketing giant WPP, Sir Martin Sorrell, in his libel claim against Italian businessmen Marco Benatti and Marco Tinelli. The pair are senior executives with Italian media company FullSix, which WPP owns a stake in. Benatti was a senior consultant to WPP until an acrimonious split in 2006.

Carter Ruck, whose team is being led by media partner Mark Thomson, has instructed 5 Raymond Buildings' Desmond Browne QC and David Sherborne.

Herbert Smith partner Alan Watts is leading the team for Benatti and Tinelli, alongside One Brick Court's Andrew Caldecott QC and Stephen Suttle QC.

The case is being closely watched as one of the first defamation actions to concentrate on blogs and e-traffic, with Sorrell's team arguing that Benatti and Tinelli libelled him and one of his WPP colleagues, Daniela Weber, in a series of anonymous online articles.

Sorrell is arguing libel and breach of privacy through the blog postings, related emailed links and an offensive jpeg image – one of the first attempts of its kind to combine traditional libel and privacy cases.

Olswang media partner Dan Tench told Legal Week: "Although people assume they will be anonymous when publishing blogs on the internet, with rigour and hard work they can often be revealed."

Reynolds Porter Chamberlain defamation and IP heavyweight David Hooper commented: "Emails and blogs are not as anonymous as people think. They have the indiscretion of a phone call, coupled with the permanence of a letter; therefore you have the worst of both worlds."

Benatti and Tinelli contest the claim and deny any personal responsibility for either the blog postings or the offensive picture. The case, which began trial without a jury last week (14 March) before Mr Justice Eady, is expected to last between two and four weeks.