God did not create the universe, the man who is arguably Britain's most famous living scientist says in a forthcoming book.

In the new work, The Grand Design, Professor Stephen Hawking argues that the Big Bang, rather than occurring following the intervention of a divine being, was inevitable due to the law of gravity.

In his 1988 book, A Brief History of Time, Hawking had seemed to accept the role of God in the creation of the universe. But in the new text, co-written with American physicist Leonard Mlodinow, he said new theories showed a creator is "not necessary".

The Grand Design, an extract of which appears in the Times today, sets out to contest Sir Isaac Newton's belief that the universe must have been designed by God as it could not have been created out of chaos.

"Because there is a law such as gravity, the universe can and will create itself from nothing," he writes. "Spontaneous creation is the reason there is something rather than nothing, why the universe exists, why we exist.

"It is not necessary to invoke God to light the blue touch paper and set the universe going."

In the forthcoming book, published on 9 September, Hawking says that M-theory, a form of string theory, will achieve this goal: "M-theory is the unified theory Einstein was hoping to find," he theorises.

"The fact that we human beings – who are ourselves mere collections of fundamental particles of nature – have been able to come this close to an understanding of the laws governing us and our universe is a great triumph."

Hawking says the first blow to Newton's belief that the universe could not have arisen from chaos was the observation in 1992 of a planet orbiting a star other than our Sun. "That makes the coincidences of our planetary conditions – the single sun, the lucky combination of Earth-sun distance and solar mass – far less remarkable, and far less compelling as evidence that the Earth was carefully designed just to please us human beings," he writes.

Hawking had previously appeared to accept the role of God in the creation of the universe. Writing in his bestseller A Brief History Of Time in 1988, he said: "If we discover a complete theory, it would be the ultimate triumph of human reason – for then we should know the mind of God."

Hawking resigned as Lucasian Professor of Mathematics at Cambridge University last year after 30 years in the position.