Train sets are highly collectable and there is a good market for them. So how much might your old train set be worth?

Mr Paul Campbell, head of the collectors' department at Sotheby's in Sussex, says that "any" locomotive of the 19001910 period will be valuable.

The first toy trains came onto the market around 1900. Powered by methylated spirits, they ran on live steam power. But while children and the young-at-heart loved them in equal measure, they were "not a safe toy for children". In fact, they were "highly dangerous", says Mr Campbell.

If they were going too fast, the "wagons tipped off at curves", carpet stains and burns were "not uncommon" and playing with them was "certainly a hazardous undertaking".

These early trains were usually "gauge 1" , that is, the distance apart of the tracks was one and three-quarter inches.

Mr Campbell explains these are "highly collectable these days". Even the more battered ones should fetch £500 sterling, while a locomotive in excellent condition could be worth £2,500.

A safer alternative was the gauge 1 clockwork train which emerged between 1900 and 1910. These were mainly German. Makers included Gebruder Bing and Gebruder Marklin. While condition is important, these clockwork locomotives even in poor condition should fetch £300 while better kept models can fetch up to £2,000.

Electric trains were introduced around 1910 and proved very popular. These were smaller "gauge O" trains with the tracks one and a quarter inches apart. They were the most popular size until the outbreak of the second world war.

Frank Hornby began producing clockwork locomotives in gauge O from about 1920. These were a "tremendous success", being "simple, cheap and cheerful".

Nowadays, a 1920s Hornby locomotive is worth in the region of £200 to £300. Boxes can add significantly to values. Mr Campbell says: "To the collector, the toy is incomplete without its box."

But by the 1930s, Hornby produced considerably better models

"handsome machines" which were "quite complete and true to form". This was the golden age of Hornby trains. Hornby locomotives from the 1930s vary in value from £300 to £2,000, depending on type and condition. For example, the School's Class Southern Region locomotive, "Eton", and the "Princess Elizabeth", which date from the later 1930s, are highly sought-after. The electric versions of each can be worth between £1,500 and £2,000.

German toy trains between the wars were distributed in Britain by a company called BassettLowke, many of which must have made their way to Ireland. These toys are now worth between £300 and £1,000.

The so-called "double O gauge", introduced around 1938, took off as the most popular size after the war. Hornby made a pun on `double O' and called their small scale, miniature toy rail system models "Dublo". Before the war, locomotives were made of tinplate, but now they were able to die-cast the models and "lovely detail was possible".

This was the era of mass production with fewer rarities, so values tend to be lower. "One can buy quite a nice Hornby Dublo locomotive for £50. One can also pay up to £500 or £600 for a good model in good condition," says Mr Campbell.

Readers can estimate the value of their own trains from the guide prices for the latest Sotheby's toys sale.

These include:

a rare German Bassett-Lowke gauge II clockwork tank locomotive. Guide price: £1,000-£1,250;

a German Bing gauge II steam express locomotive, from about 1904. Guide price: £900-£1,200;

a Bing gauge I clockwork Pacific locomotive and tender from 1914. Guide price £400-£600;

a gauge O Hornby Series €320 `Caerphilly Castle' locomotive from 1938. Guide price: £250-£350;

a Hornby Dublo 3226 `City of Liverpool' locomotive. Guide price: £200-£300;

two rare Hornby Dublo Restaurant Cars, 1963-64. Guide: £150-£200.