Chris Beetles, at his gallery in London's St James's, is the world's foremost dealer in illustrations and cartoons - not lithographs or prints but original drawings and paintings. Each year he holds a two-month sale of well over 500 illustrations and this year's show, just ending, realised more than £700,000

The items range from Georgians such as Thomas Rowlandson and Isaac and Robert Cruikshank, by way of Victorian illustrators such as Edward Lear and Arthur Rackham, Winnie the Pooh illustrator EH Shephard, to 20th century cartoonists like Ronald Searle, David Low and Frank Dickens. They include political cartoonists from Punch, John Leech and Sir John Tenniel and illustrators such as Kate Greenaway and Mabel Lucie Atwell.

The shows, however, are just the tip of the iceberg. Mr Beetles has been collecting and buying for a long time and has the largest archive anywhere. He writes books and articles and, for more than 20 years, has worked to popularise what he believes is an undervalued area of English art.

His originals have clearly been shrewdly amassed and prices for original illustrations have rocketed in recent years. Any Winnie the Pooh illustration by EH Shephard would now fetch anything from £50,000 to £125,000 at auction, depending on condition and rarity - twice or even three times what they would have realised five years ago. Similarly, Arthur Rackham pieces can realise £30,000 against £10,000 years ago.

But most are still affordable. Pen ink or drawings by Arthur Rackham can be bought for a few hundred pounds. A cartoon by Sir John Tenniel, who lived a long life and was extremely prolific, would cost between £500 to £1,000, a lot more than five years ago. Mr Beetles reckons prices have been rising by 20% a year.

Now, in collaboration with Sotheby's, he is holding his first online sale which runs from Wednesday February 7 to Wednesday February 28. There will be 100 lots reflecting a wide range of artists. Most are modestly priced, ranging from a few hundred dollars to several thousand and there are no really expensive pieces.

Why is he going on to the internet? "I have a lot of illustrations which nobody sees and view the internet as a new and exciting vehicle for promoting and selling them. They are affordable and lend themselves very well to digital reproduction. Cartoons have bold colours and strong lines."

Sotheby's has been holding internet-only auctions for a year. A unique feature of the sales is that associates, namely dealers and smaller auctioneers, can participate in auctions that would have once been exclusively supplied through Sotheby's. Mr Beetles has become another of the 4,000 associates.

Sotheby's research shows that the majority of online bidders are not normally Sotheby's clients.

Moreover, 80% of bidders are from the US. Mr Beetles has been selling more and more pieces to American collectors, particularly in New York and New England. This sale therefore, in theory, offers the chance for him to push into new areas and expand in established growth markets.

But there is a danger in going online. I put it to him that, in tracking previous online sales, I noticed that everyone seemed to wait until the last minute before bidding and that there seemed to be a preponderance of dealers, rather than collectors. Sotheby's confirmed that 80% of bids came within the last hours of an internet auction. This tended, it seemed to me, to act as a dampener on prices. The Royal Doulton sale before Christmas ran from December 5 to December 29, but on December 27 half the lots were still open and most bids were around or slightly below the estimates.

Has Mr Beetles put the less expensive pieces on the sale? "Well yes," he says, adding: "There would be little point putting an EH Shephard Winnie up for sale because I suspect I would find the difference between the buying and selling price too small. There is a risk, frankly, that I will be selling pieces for little more than I paid for them, or even as loss-leaders to publicise the art form. But I am interested in finding out."

• For further information telephone Sothebys 0202 7293 6185. Or telephone the Chris Beetles Gallery 020 7839 7551.