Toby jugs are highly collectible, can be worth well into four figures, and are popular in Ireland and abroad.

Mr Denis Drum, a porcelain specialist based in Malahide, says: "There are lots of people who collect them. I met a woman recently when I was giving a talk and she had over 200 toby jugs. They're popular in Ireland, but hugely popular in England and in the United States."

Even recent toby jugs can be valuable. A limited edition toby jug from 1992 was recently valued at £500 to £700, while a Royal Doulton advertising bull dog from the 1940s fetched £1,950 sterling at auction a few weeks ago, he says.

Mr Phil Howell, head of the ceramics department at Sotheby's in Sussex, says toby jugs from the late 18th century tend to fetch between £500 and £700, although rarer examples can fetch several thousand; those from the early 19th century tend to fetch between £200 and £500; while some from the 20th century can be worth up to £3,000.

Toby jugs stem from the later part of the 18th century, possibly based on a drunk of the day named Toby Fillpot, who is referred to in the late 18th century poem The Brown Jug.

Toby jugs are full-length jugs - unlike character jugs which are only of the head of a character. The first versions were usually made in creamware - a refined earthenware body.

The ordinary toby jug is a seated figure with a tricorn hat, waistjacket and coat, with a jug of ale in one hand and a glass in the other. But variations include the Hearty Good Fellow (a standing version); the Sailor, sitting on a chest; and the Squire - "he's quite a distinguished-looking bloke, sitting with a church warden pipe, a long pipe, in one hand. He's a collectible one," says Mr Howell.

Initially, toby jugs may have had a functional purpose - for drinking ale - but "soon they became more a decorative object".

Average toby jugs from the late 18th century fetch between £500 and £700 sterling. "But if there's any kind of damage to them, it is reflected in their price." The early ones, from the late 18th century, have translucent coloured glazes running down the body.

"Once you get into the 19th century, the glazes are more solid. They're what's called enamel coloured - they're painted on top of the glaze. So that's one way of distinguishing a late 18th century one from a 19th century one." Early 19th century toby jugs are usually worth £200 to £400. But the so-called Pratt-type from this period - with distinctive colours of blue, ochre or brown under the glaze - can fetch between £400 and £500, Mr Howell says.

"Normally, you won't find factory marks on early toby jugs, although there are some exceptions to the rule. Whereas the later ones, into the late 19th and 20th century, usually have the factory mark printed underneath." If England or Scotland is printed underneath, it dates from after 1891. This will affect its value because the earlier ones are more sought-after, he says.

However, even 20th century toby jugs can be valuable. For instance, Royal Doulton did one of Charlie Chaplin which can make between £2,000 and £3,000 sterling.

There was a series made by Wilkinson, a Staffordshire factory, of first World War allied commanders, produced between 1915 and 1919. There were 11 different figures such as Admiral Beatty, Field-Marshall Haig, General Botha and Lord Kitchener.

Mr Howell says: "If you had the whole set, they can make between £3,000 and £4,000. Individually, some of them tend to be a bit more sought-after than the others. But individually they tend to be worth about £250 each."

Royal Doulton did a toby jug of Winston Churchill, seated, wearing a long, brown coat. But because they were made in large quantities, they're only worth about £50.