Paul Henke, who had confirmed making a complaint about a colleague to this newspaper, has been barred from the party until his 163rd birthday.
Ukip, the anti-European Union anti-immigration party led by Nigel Farage, has enjoyed electoral success in England and Wales but is in the throes of a civil war north of the Border.
Until late last year, Lord Monckton was Ukip Scotland's leader and Mike Scott-Hayward its chairman. However, the party was plunged into chaos after a trio of members - including former by-election candidate Otto Inglis - were suspected of planning a takeover. The infighting came to a head during Ukip Scotland's internal selection for the European Parliament contest, during which six of the nine shortlisted candidates quit before ballot papers were sent.
David Coburn, who was chairman of Ukip in London, won the contest.
Farage fired Monckton by email and Scott-Hayward quit in a gesture of solidarity with the sacked leader.
The tensions escalated after 10 members signed a complaint against Coburn, in which they alleged he had made various false statements. One of the signatories, 63-year-old Henke, told this newspaper: "I expect the complaint to be investigated properly. I believe Ukip to be an up-front party run by honourable people. We should have honourable people as candidates."
Days later, national Ukip chairman Steve Crowther emailed Henke: "This is to you inform you that I am today suspending your membership of the party for a period of 100 years ... As a signatory of the complaint against our Scottish candidate which has been passed to the Sunday Herald, and having given your opinion on that subject to the Sunday Herald last week, you have brought the party into disrepute, and appear to be engaged in deliberately sabotaging our election campaign in Scotland."
One party source said: "Suspending him for 100 years is like a political fatwa."
The heavy sanction has prompted Monckton and seven other senior members to write to Crowther demanding the withdrawal of the suspension. They also wrote: "We regret that we must also ask for your immediate resignation as party chairman, on grounds of long-standing prejudice which now oversteps the bounds into malice - a malice that has needlessly brought Ukip into disrepute."
They also contrasted Henke's comments to the Sunday Herald with the statements of interim Scottish chairman Misty Thackeray, who said Glasgow City Council was for "gays, Catholics [and] communists". They wrote: "Why have you not suspended him from membership for 100,000 years?"
Responding to Monckton, Crowther stated in an email: "Paul [Henke] initiated the complaint, and so is responsible for its appearance in the Sunday Herald. This self-indulgent nonsense must stop."
Ukip had hoped to win a seat in Scotland in May's Brussels election, but senior figures believe the chances are now slim.
Henke declined to comment.
Ukip was contacted for comment but failed to respond.