A scientist has calculated that there is a 67% chance that God exists.

Dr Stephen Unwin has used a 200-year-old formula to calculate the probability of the existence of an omnipotent being. Bayes' Theory is usually used to work out the likelihood of events, such as nuclear power failure, by balancing the various factors that could affect a situation.

The Manchester University graduate, who now works as a risk assessor in Ohio, said the theory starts from the assumption that God has a 50/50 chance of existing, and then factors in the evidence both for and against the notion of a higher being.

Factors that were considered included recognition of goodness, which Dr Unwin said makes the existence of God more likely, countered by things like the existence of natural evil - including earthquakes and cancer.

The unusual workings - which even take into account the existence of miracles - are set out in his new book, which includes a spreadsheet of the data used so that anyone can make the calculation themselves should they doubt its validity. The book, The Probability of God: A simple calculation that proves the ultimate truth, will be published later this month.

Dr Unwin said he was interested in bridging the gap between science and religion. He argues that rather than being a theological issue, the question of God's existence is simply a matter of statistics.

"On arriving in America I was exposed to certain religious outlooks that were somewhat of an assault upon my sensibilities - outlooks in which religion actually competes with science as an explanation of the world," he said.

"While I could not be sure, having slept through most of the cathedral services I had attended during secondary school, this did not seem like the version of faith I had remembered. In many ways, this project was for me a journey home - a reconciliation of my faith and education."

Despite his findings, Dr Unwin maintains that he is personally around 95% certain that God exists.

However, Graham Sharp, media relations director at William Hill, said there were technical problems with giving odds on the existence of God. "The problem is how you confirm the existence of God. With the Loch Ness monster we require confirmation from the Natural History Museum to pay out, but who are we going to ask about God? The church would definitely confirm his existence."

Mr Sharp said William Hill does take bets on the second coming, which currently stand at 1,000/1. For this confirmation is needed from the Archbishop of Canterbury.

"We do take bets on the second coming, whether that confirms the existence of God is up to the theologians to argue, most people wouldn't believe that, though."