A feud between Ineos chairman Jim Ratcliffe and former business partner Calum MacLean has taken a dramatic turn, with Ratcliffe now suing his Ineos co-founder and former righthand man who rose to prominence by micromanaging the industrial dispute at the Grangemouth, Scotland, refinery and chemical complex.

According to the London business newspaper City A.M, which broke the story, the multi-million pound lawsuit centers around MacLean's 2014 resignation as chief executive of Ineos Olefins and Polymers Europe to take the same job at Synthomer, formerly Yule Catto. The newspaper said MacLean, who was "raided" by the UK-based chemical company, subsequently lured away Ineos' finance executive Steve Bennett to become Synthomer's chief financial officer.

Ratcliffe is said to be seeking to cancel MacLean's severance package worth "tens of millions of pounds," as he believes the "poaching" of an Ineos executive violates the terms of the sign-off. Although most of the money is believed to have been already paid out, City said the Ineos chairman wants to withhold "the remaining millions."

In the meantime, Ratcliffe has confirmed having written to Synthomer - saying that hiring Bennett reflects "very badly" on the reputation of a company whose code of business asserts that the trust and confidence of suppliers and customers is one of its most important resources.

Having received a reply, the Swiss-based entrepreneur is now said to be "considering" his position - Ineos and Synthomer companies are entwined in several trading agreements.

Adding fuel to the dispute are reports that MacLean has an "ambitious plan" to expand into shale gas, a field in which the Ineos chief has already pledged to invest $1 billion.

The new Synthomer chief also is said to be seeking to double or even triple the size of his new employer, using the trademark aggressive takeover strategy the two erstwhile partners used to build Ineos' chemical empire, now worth $54 billion in annual sales.