LONDON - Stephen Hawking, the wheelchair-bound British physicist whose book "A Brief History Of Time" became an international best-seller, is "very ill" in hospital, Cambridge University said Monday.

Hawking, 67, achieved worldwide fame for his research, writing and television documentaries despite suffering from a form of motor neurone disease that left him disabled and dependent on a voice synthesiser to communicate.

"Professor Hawking is very ill," said a spokesman for the university, adding that the academic had been taken to a local hospital by ambulance.

Hawking has been Lucasian professor of mathematics at Cambridge, a position once held by Isaac Newton, since 1979.

His stated goal is nothing less than "a complete understanding of the universe", and his work has focused on trying to unify existing theories of the large scale universe (relativity) and the small scale universe (quantum theory).

Hawking became an international celebrity through his best-selling 1988 book on cosmology, "A Brief History Of Time", which examines complex concepts like the Big Bang and black holes in an accessible manner.

It was followed in 2001 by another book, "The Universe In A Nutshell", as well as documentaries and even cameo appearances in television shows such as "The Simpsons" and "Star Trek: The Next Generation".

He received a Commander of the Order of the British Empire, a prestigious award from Queen Elizabeth II, as well as a string of honorary degrees.

Hawking suffers from amyotrophic lateral sclerosis, or Lou Gehrig's disease, leaving him almost completely paralysed. He was diagnosed with the condition aged 22 and was not expected to survive into his 30s.

But he defied expectations to build a hugely successful academic career.

Hawking has always insisted he is determined not to let his physical condition get in the way of his work, in which he specialised in theoretical physics and quantum gravity.

"I try to lead as normal a life as possible and not think about my condition or regret the things it prevents me from doing, which are not that many," he once said.

He found himself in the media spotlight for a different reason after leaving his wife and setting up house with one of his nurses, Elaine Mason, who he married in 1995.

In 2000 and 2004, police investigated allegations that Hawking had suffered mysterious assaults, but he denied this and called it a "non story".

Arizona State University in the United States announced earlier this month that Hawking had cancelled a planned appearance on April 5 because he was recovering from a chest infection and doctors had advised him not to fly.

Earlier this year, it was reported that the Discovery Channel would screen "Stephen Hawking's Universe", a new three-part special exploring the nature of the cosmos, to be screened in 2010.

Hawking was due to retire as Lucasian professor at Cambridge this year, while staying on at the university in a different role.