The 63p stamp, created by the controversial sculptor Antony Gormley to celebrate Britain's invention of in-vitro fertilisation, features a small baby-like figure lying face-down in the corner of a concrete floor.
Pro-life lobbyists, led by the Roman Catholic Church, condemned the design, which was commissioned as part of a series of stamps to mark the millennium, for using an "inappropriate image" to glorify the "destruction" of life.
But the artist, who is best known for his 65ft Angel of the North statue, dismissed the claims, saying that his design was based on his daughter, Paloma, when she was aged six days. Gormley has said publicly that he likes his work to shock.
Speaking from his London studio, he said: "It is really to do with the vulnerability of life. It isn't actually a foetus; it is a newborn baby."
The Royal Mail, which will issue 48 stamps during 1999 to celebrate British inventions and achievements, sidestepped the row by saying the stamp was an unapproved pre-liminary design. "The preliminary choices are not guaranteed to be those that go ahead for sale," a spokesman said.
The design is part of a set of four stamps scheduled to go on sale next March to celebrate British achievements in medicine and healthcare. Royal Mail bosses will tomorrow unveil the first of 12 millennium stamp issues, due to go on sale at the rate of one a month from 12 January next year.
Peter Jennings, a fellow of the Royal Philatelic Society said: "Yet again the Royal Mail is showing a complete disregard for the public in its choice of stamp designs."Reuse content