NEW DELHI (AFP) - Popular Indian guru Swami Ramdev, who heads a global yoga empire, was detained Saturday at London's Heathrow airport and questioned for six hours by British customs officials, the Press Trust of India reported.

Ramdev, a household name among Indian television viewers who tune in regularly to his yoga shows, was quizzed when he arrived at the airport on a visitor's visa instead of on a business visa, PTI quoted sources as saying.

His spokesman, S.K. Tejarawala, said the pony-tailed Ramdev was allowed into Britain after questioning.

He dismissed as "baseless" reports the guru was questioned about carrying medicines.

"It was not clear why the yoga guru was detained for over six hours at Heathrow. He was not carrying anything with him except a small bag of personal effects," Mr Tejarawala told PTI. "It is for the British authorities to explain why he was detained."

No immediate comment was available from British authorities.

Ramdev, who is customarily dressed in saffron holy man robes, travelled to London to attend a function in the coming days organised by Patanjali Yogpeeth.

Patanjali Yogpeeth is a flagship project of Ramdev and one of the largest yoga institutes in India.

Ramdev, born in northern India to illiterate parents, is in charge of a huge yoga empire and owns an island off the coast of Scotland and a private jet. He combines spiritualism, yoga and social activism.

Lately he has been prominent in India's anti-corruption movement, promising to cleanse the country of graft, and he has been linked with the strongly Hindu nationalist movement, the Rashtriya Swayamsevak Sangh.

Hundreds of thousands of devotees attend his yoga camps across India, North America and Europe each year.