The union official whose dispute with the chemicals giant Ineos escalated to the stage where it threatened the future of the Grangemouth oil refinery has resigned from his job with the company.

Stephen Deans’ union, Unite, released a statement saying: “He has worked at Ineos for 25 years and has worked tirelessly with management to help secure the future of the Grangemouth plant, and maintain positive working relationships, on numerous occasions.”

Deans said: “Ineos Grangemouth is now entering a new period, and my own situation would only prove to be a distraction, and would cast a shadow over what we all must hope will be a prosperous long-term future for the plant.”

He said he was resigning after Ineos leaked details of private emails to the Sunday Times in an effort to smear his reputation, adding: “The hurt to my family is unforgiveable and I will not allow management to take away my dignity and self-respect any further.”

The dispute with Ineos began over allegations that Deans had used company facilities to carry out work for the Labour Party. It escalated to the extent that Unite planned strike action, at which point Ineos shut the entire site down and called in liquidators for the petrochemicals part of the business.

The dispute was settled after the union agreed to changes to pensions, a pay freeze and that it would not take strike action for three years, while Ineos agreed to invest in modernising the plant.

Unite said that without diminishing its commitment to the company’s survival plan or to the agreement made last week with Ineos, in the light of the company’s behaviour at the weekend it would consider what steps could be taken on Deans’ behalf.