Harold Gale has been fired six weeks after being suspended following the extraordinary raid on Mensa's offices in Wolverhampton by society officers including Sir Clive Sinclair, the inventor who is its chairman, during which files were seized and door locks changed.
The organisers of the raid say that they had discovered that Mr Gale, 53, who in 19 years as executive director had built up Mensa to a membership of 40,000, had been using the society's facilities and staff to run his own highly profitable business.
But Mr Gale's supporters say that his business activities were well known and had often benefited the society.
His sacking from his £59,000-a-year post will lead to a fierce row at a meeting of the nine-strong British Mensa Committee, the society's governing body, in London tomorrow at which ordinary members are allowed to speak but not vote. There may be a move to oust the officers.
He is to take Mensa to an industrial tribunal and will also sue the society for damages.
Carol Taylor, his assistant, who was also suspended but has now been offered her job back with her salary reduced from £30,000 to £17,500 will claim constructive dismissal at a tribunal.
Mr Gale, a former schoolteacher who recently bought a £46,000 Jaguar car, said last night: "I can confirm that I have been sacked."
A supporter said: "It is an outrageous decision by Mensa. He made money for himself but he made even more for the society and without all his good work over the years it would not be in the strong position in which it finds itself today."
But Sir Clive, who designed the ill-fated C5 electric car, said: "What we discovered, we felt, was a conflict of interest between Harold Gale's business activities and our own. We found that he was employing office staff on his own business activities to a major degree."
Mr Gale ran a company called Harold Gale Associates from Mensa House which has published a magazine called Mind Games for more than 10 years. He also set up the profitable Enigma puzzle phone-in which is promoted in a national newspaper.
He made no secret of any of this. Mind Games had been used to promote Sir Clive's ZX81 computer and on one occasion was sent out free to members.
One source said last night: "Mr Gale operated a system which was condoned by Mensa's officers. When a new committee member started to investigate somebody panicked and decided on this ludicrous raid."