It is fat, it represents Pounds 1.5 billion a year and it might just have a little for your next research project.

The Directory of Grant Making Trusts lists trusts concerned with every imaginable cause from "the furtherance of God's work" to "projects relating to the interaction of mathematics and physical science with philosophy".

Their names are as colourful: there is the Abraham Algy Bloom Foundation, the Old Codgers Appeal Fund and the Old Possum's Practical Trust. Their grants range from Pounds 500 to Pounds 150 million per year.

But getting hold of the money is not easy. First, a lot of it goes directly to universities and research charities - the ones who can show that they will distribute it according to the trust's manifesto.

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Second, says Anne Villemur, editor of the directory, trusts are asked for more and more each year: "They are increasingly hard-pushed to fund even the things they want to fund."

Nevertheless, if you have a trait that makes you obscure, a member of a minority or under-privileged, and you want to do a taught course, it is worth spending an evening flicking through the directory to find funding. There is a trust for impoverished orphans of gardeners and there is one for women under 25 "lately residing in or near Brighton".

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If it is research funding you want, trusts fund subjects including the humanities, sciences and education research.

Trusts are set up by companies and by wealthy individuals. But, despite their charitable outlooks many protested against being publicised by the book when it was launched in 1968.

Publicity generates a huge number of unfocused pleading letters. Small trusts may even begrudge the secretarial time spent tearing open envelopes that carry requests to support causes irrelevant to what they are permitted to fund. One charity that only supports applications from Northern Ireland, for example, receives a third of its applications from Great Britain.

The trusts' resentment stands out on every page of the directory: "unsolicited applications will be thrown out unopened"; "no applications wanted that are obviously mail-shots". Ms Villemur has had bags of unwanted letters forwarded to her by a particularly irritated charity.

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So the first rule is to be selective. Next, take care of grammar. One trustee is reputed to immediately throw out any letter that contains a split infinitive.

Third, make your letter specific to that trust. Do not copy the student who wrote to trusts explaining that he had been sent a bunch of address labels by his Welsh university and their address was among them. Do not write enclosing your bank account number, which has also been tried and has failed.

There are several ways in which you can skew the content of your research proposal to be more attractive to trusts.

Nigel Siederer, director of the Association of Charitable Foundations, says: "You need to convince the foundations that the research is of importance for the outer world. Trusts' research funding is about improving the world."

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Ms Villemur says: "Trusts tend to stay away from anything the public would be likely to fund or would get support from corporate donors."

Finally, demonstrate that your proposal carries weight by getting authorisation from your university, perhaps in the form of a letter supporting your ideas, says Mr Siederer.

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