Sir Martin Sorrell’s departure from WPP has descended even further after lawyers for the company he founded were called in.

Sorrell, of course, left WPP abruptly in April amid allegations of impropriety and he has since manoeuvred to start his own media business apparently in direct competition with WPP’s offerings.

His first potential takeover target was a $536 million buyout of the Dutch-based digital production business MediaMonks. However, MediaMonks is fielding offers from a number of other potential buyers, including WPP.

WPP believes that Sorrell’s overtures towards MediaMonks are “likely to be in breach of his confidentiality obligations” when he left the business and its lawyers have said it will withhold £20 million ($A36 million) in future payouts Sorrell is owed by WPP if he progresses with any potential takeover.

When Sorrell left WPP under a cloud of personal misconduct it was deemed he’d retired and would be paid the $36 million over the next decade based on payouts relating to share awards.

Both Sorrell and WPP have declined to comment on the matter thus far. However, Sorrell’s lawyers are disputing the claims and asking for WPP to provide evidence for its allegations.

The 74-year-old Sorrell had previously said that he would not compete against WPP, however, industry commentators think that is highly unlikely due to his competitive nature.

Sorrell has labelled his next venture as a “next generation” advertising group and is reportedly building a £1 billion ($A1.8 billion) war chest from investors to start and future-proof the project.