The company may have been forced to cut ties with Irish organisations and functions because of the IRA bombing campaign, public relations chief Edward Guinness told embassy officials in London.
The rebranding plan was prepared on the back of deepening resentment of Ireland and Irish brands in Britain, he said.
"Mr Guinness remarked that an association with Ireland was part of the Guinness image," Paul D Dempsey of the embassy wrote. "He was no longer sure this association with Ireland was helpful.
"They were encountering a lot of resistance to the Irish angle and this could force them to emphasise facts such as that Guinness was an English company which had its base at Park Royal. Indeed they had publicity material of this kind ready during the Falklands crisis, but had not used it."