If you're spring cleaning this weekend, check that box of old books before dropping them off at the charity shop or, disgracefully, into the neighbour's skip. You might just be throwing away a fortune.
Perhaps you vaguely recollect a long-forgotten rich ancestor with a penchant for ornithology and you possess a large attic. A long shot admittedly, but if there's a copy of Audubon's Birds of America up there, congratulations. Published in the early 19th century, the last complete set of this celebrated four-volume work sold to an American buyer in London two years ago for $8.8 million. Before reaching for the stepladder you should be aware that the chances of finding such books fall into the realm of Lotto rollovers. But there are many gems languishing unnoticed.
With increasing affluence, more Irish people are taking an interest in our "collectable" heritage and, appropriately for a country which accords such prestige to literature, books are proving to be an increasingly shrewd investment. Wealthy Irish collectors living abroad and admirers of Irish literature around the world are also fuelling demand.
According to Fonsie Mealy, Ireland's leading rare book auctioneer, "there's a lot of money out there in the Irish diaspora". Mr Mealy, head of a family firm based in Castlecomer, Co Kilkenny, says antiquarian books by Irish authors in the fields of travel, science and medicine are keenly sought.
The most unexpected books can excite interest. In 1732, Richard Cantillon, an Irishman living in France, wrote a theoretical treatise on economics, Essai sur la nature du commerce en general, which was published in London after his death. Sounds dull? If you have a copy, head to Kilkenny for a valuation. Reserve a suite at Mount Juliet to recover from "sticker-shock".
When it comes to the 20th-century, James Joyce's Ulysses is the Holy Grail. At a Sotheby's New York auction in April a copy estimated at $80,000 to $100,000 sold for $288,000. However, the real drama in Manhattan was provided by Yeats. A copy of his 1928 collection of poems, The Tower, reached a hammer price of $108,000 - 10 times its estimate.
Both were signed first editions in very good condition but with really big-name authors even later editions can set salerooms aflutter. A Portrait of the Artist as a Young Man was first published in America in 1916. Last December, at an auction in Swindon, a copy of the first English edition of 1917, inscribed on the title page "James Joyce", was estimated to be worth £10,000 to £15,000. Although the auctioneers were "not of the opinion that the signature is indeed in the author's hand", the book was bid up to £27,000.
Of course, these prices are beyond the budgets of most book lovers and collectors. But, just as in the art world, more recent works by Irish writers are beginning to attract attention. A random selection of first edition novels offered by a Dublin bookseller last week: John Banville's 1971 Athena (€95); John McGahern's 1970 Nightlines 1976(€295); and John Broderick's 1962 The Fugitives (€125). Not yet in Joyce territory, but a significant multiple of the original price. Despite popular belief, hardback does not always mean more valuable. Roddy Doyle's The Commitments was first published in paperback in Dublin in 1987; today a pristine copy will set you back over €1,000. Go on, check your bookshelves.
Poetry does not normally sell in large quantities and Seamus Heaney is one of the only poets in the world who routinely enters the best-seller lists. The additional cachet of the Nobel Prize means his stock, in investment terms, is rising steeply. His translation of the Old English poem Beowulf, the bane of many an undergraduate's life, was a good investment in 1999. A copy in a Notting Hill, London bookshop last week carried a price tag of £550, while his 1972 collection Wintering Out was priced £1,000. The first is signed by the author but the second, though unsigned, is rarer.
Classic children's books in good condition are among the rarest and most desirable. Few survive the rigours of their unavoidable wear and tear. For once, it might be a good idea to supervise children if they decide to unclutter their rooms. If they happen to have a 1997 "de-luxe" first-edition copy of Harry Potter and the Philosopher's Stone, you could make a sizeable dent in the mortgage. The estimated current value is £25,000. This may explain why the most recent title in the series had an unprecedented first print run of well over a million copies. No doubt many an aspiring collector bought one.
In specialist London outlets, titles of Irish provenance are also rising in value. If your little darlings inherited a copy of Irish Fairy Tales by James Stephens and enchantingly illustrated by Arthur Rackham - from an enlightened forebear who bought the first edition in 1920, perhaps? - then prise it gently from their grubby hands. £3,300 and rising. However, the glittering prize in the nursery is Oscar Wilde's The Happy Prince. One of 75 signed copies is currently on sale for £13,000. Anyone out there got one of these? Treasure it and buy a modern copy for bedtime reading.
More contemporary purchasers who bought Eoin Colfer's Artemis Fowl for a child in 2001 may be tempted to steal it back. At £500 this already represents a spectacular return on investment and is tipped as a blue chip of the future.