It used to be regarded as a mainly childhood pastime but there is now a growing number of wealthy hobbyists who are discovering the lucrative pleasures of stamp collecting.

The value of Britain's 30 rarest stamps has rocketed by more than 100 per cent in five years and the profits of the world's leading philately company have soared in the past six months.

The growth in interest is partly down to the generation of forty and fiftysomethings with substantial disposable income who have taken early retirement to pursue their interests, as well as the easy access of stamps on the internet.

Rare or precious stamps are also seen as an alternative form of investment to shares or pension schemes. Stamp collections, at their highest level, are a multi-million-pound investment with some of the rarest single stamps valued at £3m. The market is attracting new investors worldwide.

While the growth is mainly at the higher end of the market where stamps can cost upwards of £1,000, there is also a rise in the hobbyist, "part-time philatelist", and the sale of stamps puts them among the top three commodities sold on eBay.

Stanley Gibbons stamp dealers have seen profits rise by 23 per cent in six months. Richard Purkis, a director at Stanley Gibbons, said the market had sped up over the past three years. "Stamps are an ideal internet commodity," he said. "You can see everything and they are incredibly light, so easy to transport."

David Beech, head of philatelic collections at the British Library, which has the largest and most expensive collection in the world, said serious collectors were just as interested in a stamp for its watermark, perforations and colours as the illustration on the stamp.

"It is about a love of collecting, a love of history and the thrill of the chase in finding something at auctions or dealers," he said.

British stamps have a "heritage" value as stamps were invented here in 1840. The Four Anna stamp of India, from 1854, was bought in 1890 for £32 and is now considered priceless, while the Tre Skilling Banco Yellow, the only known stamp of its kind in yellow, sold for £2.5m in 1998.