There are a few things in the newspapers that mention The Tack Organisation.
From what I've gleaned it seemed to be some sort of sales persons organisation and business.
Basically, there are various adverts from the 50s to the 90s, that speak of getting you to sell products to schools and businesses and joining their training school, which was at Longmore Street, London, amongst other addresses. There is also mention of the Tack School of Salesmanship, and a public speaking course. It seems to be mostly about business people and salesmanship skills.
By the 1990s the adverts say there were 40 branches of the school world wide.
There is no mention I could find in the 2000 - 2009 period.
So I would guess that perhaps your relative went on a course at some point, or perhaps even delivered training?