The two have launched legal claims against each other with WPP seeking £5.7m payment for work done on the launch of OK! in the US. Desmond is counter-suing and seeking up to £5.5m from WPP over claims that the group guaranteed ads for the launch.
The autumn launch was being touted as the biggest in US publishing history, with Desmond claiming he had committed a $100m (£57m) budget to the launch, part of which was used for Beattie McGuinness Bungay's television, press and poster ads.
Desmond claims that WPP's MediaCom demanded an increase in Express Newspapers' TV adspend in return for the media buying agency's support in putting its clients' advertising in the title to the tune of 15 pages every week.
WPP denies Desmond's claims although the deal would not be an unusual one.
The news comes as Sorrell's problems over WPP Italy mount. The company's Italian country manager, Marco Benatti, is suing WPP after he was forced out the company. It has been reported that several senior executives could also lose their jobs following the start of legal proceedings against Benatti.
WPP is demanding an explanation of "irregular personal expenses" paid by WPP Italy-owned companies to several clients and media owners. Tension between Sorrell and Benatti began over the latter's financial interests in Mediaclub, which WPP acquired after Benatti introduced the media company to the group for a fee.
Benatti has demanded €8.9m in additional commissions relating to Mediaclub, a figure which WPP says should be only €350,000.
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