Bob Paisley suffered from dementia

He claims later research done in Norway did not account for other factors that could have contributed to neurological disorders, such as previous head injuries, drug or alcohol problems, learning disabilities and other factors.

He said: "The consensus of what we see today is that the force of impact from heading a soccer ball is fairly low.

"Players prepare for heading the ball by tensing up their neck muscles and in effect put their entire body into the heading motion.

"We're not talking here about accidents in which the ball strikes someone's unprepared head."

Further research

The conclusions have been welcomed by the Professional Footballers' Association (PFA), which is carrying out its own research into any possible risk of brain damage associated with heading the ball.

Director of the PFA Gordon Taylor said: "It's good news, but until we check the strength of the research, we have chosen to do our own research over a number of years to track our younger players."

The 24 young players taking part in the project will undergo tests and brain scans, monitored at five yearly intervals.

Mr Taylor said: "We have had a number of well known former players, including Joe Mercer and Bob Paisley, who played football and then in their latter years had problems with dementia and a number of people pointed out to us that it could have been linked to football."

Dr Kirkendall accepted that head injuries were possible in football, but resulted chiefly from players falling down, kicking one another, colliding with someone or running into a goal post.