Accountant David Riley, 55, from Accrington in Lancashire, has become an expert on horror fiction from the 1970s. Having collected these books since his late teens, he has reduced his hoard from several thousand to around 500, as he and his wife plan to settle in Bulgaria later this year. Riley writes horror fiction and his wife runs a second-hand bookshop.

His own collection of horror stories, The Lurkers in the Abyss, (Midnight House), is due to be published in the US in the spring. “The market for horror fiction in the US is now stronger than here,” he says.

“While my collection is worth around £10,000, the average value per book is £3 to £5. It is the obscure hardbacks that are valuable. If I do decide to part with the rest, I will sell them off in batches of 50 or 100 on eBay.”

In 1974 James Herbert published The Rats, which reinvented the British horror novel with its unprecedented level of violence. Other authors followed, such as Guy N. Smith who wrote about killer crabs, although it is his earlier works that are highly prized as not many copies have survived. However, because Herbert has sold around 50m books, he is not collectable. The authors who become collectable are those who wrote books that did not sell at the time, but who acquired a cult of devotees.

Riley points out: “The World by Moonlight, a werewolf story by Guy N. Smith, published in 1974, could fetch up to £50 for the paperback. It was not published in vast numbers and is very difficult to get hold of. The paperback has a value of £40. Few people in those days would have saved these books. They were the kind of books you would have read on a train and thrown away afterwards.

“Quite honestly, Smith was not a particularly good writer but he was prolific, churning out at least 40 or 50 books.”

Riley has read many of the novels in his collection. He bought at least 60 per cent of his books at the time of publication. Two names to look out for are Raymond Giles and Graham Masterton. Giles wrote a number of Sabrehill novels that today are worth about £10 each. The Heirloom by Graham Masterton, published in 1981, is worth £25.

The paperback of Stephen King’s first novel Carrie, published in 1975, is only worth a few pounds, but the hardback is another matter: £1,000 or more for the first US hardback edition published by Doubleday in 1974. It was printed in small numbers as the publishers did not realise they had found a best-selling author.

Riley says Dennis Wheatley is now resurgent. “For a good quality first edition in hardback, you are talking about £100, and he wrote more than 50 books, including historical novels. One of his most collectable 1970s novels is The Irish Witch, worth £8 to £10 in paperback.

“The market is changing. A few years ago you would have paid £20 or £30 per hardback book. Today it would be anything from £30 to £40 and possibly more because he is in favour again.”

Other collectable authors are Shaun Hutson, who wrote about killer slugs, and Ramsey Campbell. Riley bought one of Campbell’s early hardbacks in the 60s, The Inhabitants of the Lake. Published in the US in 1964, it is worth several hundred pounds today. Riley says: “I own another of Ramsey’s books, The Face That Must Die, published in 1979 by Star Books, that is worth £40 in paperback. I have seen the hardback for sale online for £150 to £200. If I had known these books were going to become collectable I would have saved absolutely everything. Many books I sold or gave away.

“The only novels not worth anything at all are book club editions. It is very rare that they have any kind of value.”

Ironically, the 1970s book Riley has made the most money from is not horror fiction, but a Patrick O’Brian novel, The Surgeon’s Mate. He bought the first hardback edition new in 1974 and sold it two years ago on eBay for his reserve price of £900.

Alwyn W. Turner, 45, a social historian of the 1970s, says: “The reason these books are collectable is a nostalgia value to the Baby Boom generation who read them. Generally it is not individual authors who are worth a lot in their own right. The value is focused on specific books. Most people who like these horror books are not interested in selling them. I buy them to read, not to sell.”

Riley runs a website, www.trashfiction.co.uk, where he has reviewed 500 books from the 1970s, of which 100 are horror fiction. He says: “One Stephen King book, Rage, is collectable because it was published under his pseudonym, Richard Bachman. This title is particularly sought-after because the author withdrew it from circulation.

“Published in 1977, it is the story of a high school shooting, and pre-dates the Columbine massacre. Rage could reach as much as £75. King wrote several other books under this name, but they are less collectable.”

Another collector’s item is The Pan Book of Horror Stories, which started in 1959 and came out once a year. By the early 1970s it was hugely popular, and by the mid-1980s, horror was a very big genre.

Turner says: “The final volume of this series was in 1988. The 29th volume from 1987 and the 30th from 1988 can fetch anything from £70 to £100 each.

“The reason they are worth that much money is because so many people grew up reading the Pan Book in the 1970s. The last ones are valuable because the same people want to have a set of all 30 volumes.

“Most of the volumes were printed in large numbers and had colossal sales. The last few only went into one edition and barely sold any copies. I was lucky to find a copy of volume 30 in a charity shop for 49p.”