LONDON (Reuters) - Paganism and the ancient art of witchcraft are on the rise in Britain, experts said on Thursday as the summer's most celebrated Pagan festival approached.

Television, the Internet, environmentalism and even feminism have all played a role in the resurgence, they say.

Soaring Pagan numbers have churches worrying and calling for stricter controls on cult TV programs and films that celebrate sorcery like "Harry Potter," "Buffy the Vampire Slayer" and "Sabrina the Teenage Witch."

Record attendance is expected at dawn on Saturday morning at the mystical megaliths of Stonehenge, where Pagans have celebrated the summer solstice for thousands of years.

The trend has worried some of the Protestant church's more traditional elements.

"The rise of interest in Paganism is damaging because it normalizes spiritual evil by presenting it as mere fantasy and fiction," said Reverend Joel Edwards of the Evangelical Alliance, a grouping of some one million UK Christians.

"The Evangelical Alliance calls on government and TV regulatory bodies to monitor programs which promote or glamorize Pagan issues," he told Reuters.

Thirty thousand are expected to dance in the sunrise on summer's longest day at Stonehenge, says English Heritage, which manages the site -- nearly four times the number in 1990, when it re-opened to the public after many years.

Scholars believe the ring of 20-tonstones was built between 3,000 and 1,600 BC as a sacred temple. Many of the revelers will be there just to party, but among them will be druids, who believe in spiritual enlightenment through nature, and witches who practice Wicca -- harnessing nature's power as magic.

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At least 10,000 Pagan witches and 6,000 Pagan druids were practicing in Britain at the last estimate in 1996, said history professor Ronald Hutton at Bristol University. He too suggested the number was rising.

"Both the witches and the druids were always heavily outnumbered by what I'd call non-attached Pagans," he told Reuters. "There are perhaps 100,000 to 120,000 in Britain."

Paganism has been rising in the UK since the 1950s, Hutton said. "It's a religion that meets modern needs," he added. "Traditional religions have so many prohibitions: Thou shalt not do this or that. But Paganism has a message of liberation combined with good citizenship."

He pointed to the ancient Pagan motto: "An (if) it harm none, do what you will."

Matt McCabe of the Order of Bards Ovates and Druids (OBOD) said his order had grown from a few hundred in the late 1980s to 7,000 worldwide today. Much of the growth he put down to the appeal of remote learning via the World Wide Web.

"People are very reassured by the structured learning we can offer via the Web," he said.

The 1970s environmental movement also had an impact, said McCabe, with a lot of environmentalists attracted to Paganism because of its veneration of nature.

Hutton said feminism in the 1980s had a similar effect, with women drawn to the female god-figure that is also worshipped. Then in the 1990s came the TV programs "Buffy" and "Sabrina," about teenagers with supernatural powers.

"Anything that makes teenage girls feel powerful is bound to go down well," joked OBOD's McCabe.

Kevin Carlyon, High Priest of British White Witches said "Harry Potter" in recent years had continued the trend, helping create what he called "the fastest growing belief system in the world." But it was not all good, he added.

Fresh back from a trip to Scotland to lift an old hex from the Loch Ness Monster, he warned teenagers against joining witch covens too young.

"There are some bloody weird people out there," he said.