The auction house Christie's has seen collectors paying top prices, from the black Steiff teddy bear which fetched £91,750 to the rare 1950s Masudaya Machine Man sold for £29,900 and the rare A. Marque Bebe doll dated 1913 which sold for £56,500.

If you spent £100 on Dinky toys in 1985, your investment would have likely quadrupled in value over 15 years, putting other investments in the shade.

But experts warn that investing in toys is a risky business, and the advice from Christie's toy specialist Daniel Agnew is simple: "Don't. We never recommend collecting as an investment, and it has never proved 100% reliable. There have been instances of people spending too much on tin toys in an over-inflated market."

And rushing out to buy collectors' items is a waste of time and money, argues David Nathan of Vectis, the world's largest auction house for toys. "Those special limited editions of collectors' toys you see advertised in glossy magazines are unlikely to increase in value, because every single person who buys one keeps it in mint condition. The most valuable toys now are those which were bought to be played with, and just one or two survive in good condition."

Some 25 years after toys were launched, Mr Nathan argues, the nostalgia factor kicks in. "The people who remember those toys are all adults with surplus spending power, and that drives the price up."

So while he cautions against buying toys as an investment, it's worth looking through the attic for that unwanted gift still in its box from three decades ago which might just make your fortune.

What to look for

Some toys are worth a fortune. Early American cast iron money banks and good quality dolls and teddy bears can all fetch prices exceeding £50,000, says Mr Agnew. Dinky cars and Hornby trains are often worth large sums: a rare pre-war Dinky H G Loose promotional delivery van fetched £4,600 at Christie's. Even the Dinky toys you paid three shillings and six for 40 years ago could now be worth up to £500.

A dusty attic is a good place to start, though Mr Agnew sounds a note of caution: "The best items we sell are from quite well off families, because toys were expensive. But if you are looking through the attic of Lord and Lady Somebody who were well off in the 1900s, your chances are quite good."

But the collectors' market is fickle, and something that seemed worthless a few decades ago may now be in real demand. Admitting that he has no idea which modern toys will fetch the best prices in a few decades' time, Nathan points out that early Star Wars toys are worth a packet.

And though plastic toys were once held in low esteem, the market for early Sindys, Barbies and Action Men is now growing - especially in their original boxes, and with the ephemera such as clothes and accessories.

While sought-after toys in good condition can command high prices, their value varies greatly. Factors affecting the price include age, rarity value, whether there is a market for a particular item, and above all, condition. While a mint condition toy in its original box can be worth a fortune, a battered and bedraggled version is not.

Your local toy and antique fair could be a place to pick up a valuable collector's item, though Mr Agnew is sceptical: "You have to be very careful because there are a lot of fakes around. Toy collecting is a good hobby because you meet lots of interesting people, but don't invest everything in it. My best advice is to do your research before you start. If you know what you're looking for and you have a good eye, you should do well."

Collecting modern toys

So will the Beanie Babies and McDonald's toys of today be worth a fortune in years to come? Mr Agnew thinks not, though he believes that waiting 30 years is the key: Christie's have just started selling 1970s toys.

Others toys are a better bet. The omnipresent Teletubbies might just become collectors' items in mint condition, believes Nathan, "Because people don't really think of them as collectables, and just a few will survive in good condition."

Rarity and demand ultimately determine the value of a toy, as collectors pay high prices for a toy they simply have to have.

Perhaps the best investors are businessmen: the Japanese businessman who paid a world record price of £110,000 for a teddy bear knew what he was doing - the publicity he won for his newly opened toy museum was worth millions. And although that mint boxed Barbie or Dinky may just be worth a fortune some day, the experts warn that there are safer ways to invest.