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Sir Martin Sorrell
WPP has threatened to take away share awards worth hundreds of thousands from its former chief govt Sir Martin Sorrell over his rival bid for digital manufacturing firm MediaMonks.
The BBC understands the share awards are probably worth about £20m.
Dutch agency Mediamonks is dealing with takeover bids from each WPP and Sir Martin's new S4 Capital enterprise.
A source shut to Sir Martin stated "I would say WPP are trying to muddy the waters, stir things up".
Speaking on circumstances of anonymity, the source stated that WPP's attorneys had written to Sir Martin claiming that was possible to be in breach of his confidentiality obligations.
He added: "If WPP is going to start some sort of procedural process, Sir Martin will fight it. But this guy is worth £400m to £500m. He is not going to allow £20m to stand in the way what he is trying to do."
He described relations between Sir Martin and the promoting firm he based, WPP, as "obviously not very good."
He added: "He is not out to damage WPP. He is still one of the largest, if not the largest private shareholder in WPP, so why would he want to do that?"
Sir Martin purchased WPP in 1985 and turned it into the world's greatest promoting and media firm with revenues of £15bn.
However, he stepped down as chief govt in April after the board stated it was investigating claims of misconduct.
There have been allegations relating to the use of firm funds to pay for a prostitute, which Sir Martin has denied.
WPP later stated its board had appointed unbiased counsel to conduct the investigation.
Within weeks of leaving WPP, Sir Martin had purchased a shell firm, and renamed it S4 Capital.
He described it as "a company that aims to build a multinational communication services business focused on growth."