The UK School Teachers Protection Society only has about 1,000 members, but offers a wide range of insurance services, including personal accident cover, death-in-service benefit, Pounds 1 million in public liability cover, a free legal advice helpline and free stress counselling, all for Pounds 21.50 a year.
Ivor Thomas, who founded the society, still runs it with his wife Carole from their home in Kettering, Northamptonshire, with little more equipment than a filing cabinet, a card index and a typewriter.
Mr Thomas, 58, a design and technology teacher now working part-time, says he started the society in 1970 because he was dissatisfied with the political aspect of the teaching unions.
He said: "I wanted the sort of insurance cover the unions offered as part of their membership package, but I'm not a political person, and there had been a whole series of industrial disputes around that time which I didn't support.
"I went to the insurance companies and asked them what they could offer us as a package if we put together a society of 100 or 150 members. We put an ad in The TES and it took off from there. Our members are right across the age range, but they tend to be the more mature teachers, people who have realised they can look after themselves, make their own arrangements."
The society eventually signed up with Royal Insurance, which has underwritten it ever since and provides the legal advice helpline and stress counselling. At one point membership rose to around 1,500, but Mr Thomas believes the society would lose much of its attraction if it grew too big.
He said: "We don't want to grow to 50,000 members. It doesn't take up a phenomenal amount of our time, and we can give a much more personal service to our members - people write in and say they enjoy recognising the handwriting on the envelope."