An artist who designed award-winning special edition stamps for the Royal Mail is furious after valuable work got lost in the post.

Yvonne Gilbert posted two children's illustrations using the special delivery service, confident they were in safe hands.

She had every reason to have faith in the Royal Mail - it has in the past paid her thousands of pounds to design special sets of Christmas stamps.

But three weeks on, her pictures are still "missing", and now bosses have added insult to injury by saying the illustrations are only worth the cost of the paper they are painted on. Mother-of-one Mrs Gilbert, 53, of Newcastle, said: "I am absolutely furious. These are extremely valuable pieces of art."

Mrs Glibert, who has worked on private collections for the late Princess Margaret, had been commissioned to complete the illustrations for publishing firm Templar.

The coloured-pen designs were set to illustrate new children's book 'Wizardology', and pictured Merlin in his book-filled study, and a young magician in training.

Mrs Gilbert posted them at Gosforth post office, Newcastle, telling counter staff what they were and how much they were worth. She says she was told they would be tracked and covered.

But when they failed to turn up she called Royal Mail to be told they were "missing". She said: "They took me a week and a half each to do, but Royal Mail just couldn't care less. Rather than look for them their attitude is just wait and claim compensation."

But the artist, who lives with her fiance, a graphic designer, said that when she did try to put in a claim, she faced repeated questions about what was in the package.

She said: "They've done their upmost to prove it's worth no money at all.

They say as far as they're concerned it's worth the paper it's on and the ink I used. No more. "But it's worth about £2,500. Not to mention its future value if the book is a success."

Mrs Gilbert said the attitude was astonishing, especially considering the company has paid her more than £100,000 over the years to design five sets of special stamps.

For her last commission, for five stamps at Christmas, 1991, she recieved £20,000. "That was just for five small pictures", she said. "So they know the going rate."

A set commissioned in 1984 later won the company two prestigious global awards, including the highly-prized Golden Stamp and Most Beautiful Stamp accolades.

"They went missing at the supposedly secure London depot in Gatwick, but they won't let me look for them. I don't understand where they can go when it's only their staff there," Mrs Gilbert added. And now she is calling on the company to make clear its policy for calculating the value of art work, to save other illustrators and designers the same heartache.

A Royal Mail spokesperson said yesterday: "We take all customer complaints seriously. We are investigating Yvonne Gilbert's case and hope to resolve the matter as soon as possible."