Pianos are becoming more and more valuable, according to Mr Richard Reason, a specialist at Phillips auctioneers who maintains that the piano auctions organised by the company at Bayswater in London are "the biggest" in the world.

Quite a lot of people come over from Ireland to buy, he says, with the next auction on October 4th.

To estimate how much your piano is worth*, "the maker's name is the important thing", with the many leading names including Steinway, Bechstein and Bluthner.

There are two other big distinctions - straight-strung and overstrung pianos. "You can tell straight-strung pianos because all the strings run parallel to one another."

But the better pianos are overstrung, "where basically the strings on the left-hand side run at one angle over the top of the ones on the right-hand side - they cross over". So, if you don't already know, look in the top of your upright piano to see which type you have. And now for the bad news: "In general terms - and this is layman's talk - if it's straight-strung, forget it. It needs to be overstrung," Mr Reason says. But a word of caution: there are exceptions to the rule "if we're talking of historic pianos or anything like that".

The same is true for grand pianos. And of course it's much easier to see whether a grand piano is straight-strung or overstrung because you only have to lift the lid.

As with uprights, historic pianos are exceptions to the rule. "But for a piano to be historic it's fairly rare and you're talking about something that's got to be 1800 or earlier."

The ones that "everybody thinks are worth a fortune but are not" are straight-strung Broadwood grands. Mr Reason has to break this news to as many as one in eight enquirers. These usually nice-looking pianos were made "in vast numbers" from about 1850 to about 1885. "But they're straight-strung and they're only worth about £200 [sterling (€311)] or so. That makes quite a few people unhappy," he says. He believes that many of these would have ended up in Dublin and in country houses in Ireland.

If you have an ordinary 1920s Steinway grand of about six feet, it should be worth between £5,000 and £8,000 sterling. And that, he stresses, is regardless of its condition, "whatever the condition - really - because they get rebuilt".

And as for Steinway pianos with decorative cases, "the sky is the limit. Because you've got the best name, in cases that could never be repeated". A recent, nicely inlaid Steinway grand, sold at Phillips for £23,000 sterling, while an early Steinway grand fetched £50,000.

If you have a Steinway upright, its age is important. One 1920s model that always had the letter K inside, "will always make £1,500 to £2,000". The 1920s were the golden age of Steinway. Generally, earlier ones will fetch slightly less.

The very early pianos from 1760 to 1800 are "worth very serious money". A Dublin-made upright by one John Robert Woffington dating from circa 1800 fetched £6,400 sterling at the last Phillips auction. "It was a cottage industry at that stage, so you did have the odd maker in Dublin," he says.

Bechstein grands tend to fetch £2,500 to £4,000 but be warned that pre-1914 grands should be only £1,000 to £2,000, he says. Bechstein uprights are very complicated because they made lots of different models but a 1920s model should be about £1,000 to £1,500.

* Readers can contact Mr Richard Reason to value their pianos between 9 a.m. and 1 p.m. on weekdays by telephoning 0044 1462 450 367.