Professor Willie Stewart said on the balance of probabilities, head impacts were leading to long-lasting brain injuries in athletes across a range of sports, but said it would be a “virtual impossibility” to prove beyond a reasonable doubt.

Stewart was speaking to MPs on the Digital, Culture, Media and Sport (DCMS) committee as they held their first evidence session on Tuesday morning ahead of a new parliamentary inquiry into concussion.

In 2019, the FIELD study which Stewart led found professional footballers were three-and-a-half times more likely to die of neurodegenerative disease than age-matched members of the general population.

Stewart also examined the brain of England World Cup winner Nobby Stiles following his death in October last year and concluded that Stiles had been suffering from CTE, which is only found in people with a history of repetitive head trauma.

Stewart told MPs: “We take the position that the only thing that connects football to American football to boxing to rugby to wrestling to other sports where we have seen this pathology is head impact and head injury exposure.

“There must be something else because people can have exposure to head injury, people can play the sport the same way and don’t develop problems, there must be other things contributing to it, but the one common factor is this head injury.

“To prove it beyond a reasonable doubt as opposed to on the balance of probabilities is a virtual impossibility, because the exposure is in their 20s and the outcome is 30, 40 years later. It is vanishingly difficult to prove beyond a reasonable doubt, but on the balance of probabilities I think we’re there.”

Asked by MP Kevin Brennan whether rugby was safe, Stewart said: “I think it could be made a lot safer, there are things to be done to reduce the risk of head injury.

“It’s a contact and collision sport, but there are aspects of it that could undoubtedly be improved.

“I know a lot of people who work within rugby at a national and international level on the medical side and the performance side who are wrestling with this issue.

“On the one hand, the global business, the industry, there is a revelling in the collisions and the contact, but it’s doing a lot of damage to young men and women so they are desperately trying to find a solution.”

Stewart described football’s management of concussion as a “shambles”.

The game’s lawmakers, the International Football Association Board, has drawn up protocols which have led to trials of permanent concussion substitutes taking place, including in the Premier League and the FA Cup.

Stewart criticised football’s approach, saying it should have followed rugby’s model in which temporary substitutes come on while a player’s head injury is assessed.

“Football has a habit, whenever it is forced to develop, of going out on their own and trying to develop something unique to everybody else as if the problem never occurred before,” he said.

“What football has introduced is a shambles in 2021.”

Asked whether temporary substitutions were preferable, Stewart added: “Unquestionably. Rugby has made great developments in understanding how you can assess and identify players with brain injury on the field, and that should be the model and the benchmark that (other) sports start from.

“They shouldn’t be starting with a blank page and drawing up a protocol, they should just be saying ‘how do we make that happen in football?’.

Stewart was asked by committee chair Julian Knight what he could do with £2.3million of additional funding, and he replied by saying that the work done on the FIELD study had been achieved with about 10 per cent of that.

Knight said the £2.3million figure was the annual salary of Professional Footballers’ Association chief executive Gordon Taylor, who has been criticised by head injury campaigner Dawn Astle among others for not acting quickly enough to commission research in this area.

Peter McCabe, the chief executive of the brain injury association Headway, cited an incident at Manchester United where West Ham defender Issa Diop suffered a head injury but was allowed to play on until half-time.

The Frenchman came off at the interval, becoming the first player in England to be replaced by a concussion substitute.

“Within a few days of introducing that protocol there was a poor example,” McCabe said.

“The player was assessed for two minutes on the pitch and then allowed to carry on for a further seven minutes until half-time and then substituted using the new protocols. We think that highlights the weakness of that system.

“There’s another factor and that is if you’ve only got two minutes, and you’ve got multiple languages spoken in the Premier League, how can you assess someone?

“You take them off the pitch and there can be a translator available to help with that assessment. For all those reasons that needs to be looked at as a matter of urgency.”

Richard Oakley, head of research at the Alzheimer’s Society, said sporting governing bodies have a duty of care for their members.

“We have to reduce the risk and we are sharing information. That’s why the sporting bodies are so important,” he said.

“There’s a huge question about those in mid of later-life. The best way for anyone worried about their condition is to go to a support line and get the best advice.

“We are having the meetings and those discussions. The FA and Premiership Rugby, the fact that everyone is coming together and raising the profile is a good thing. It’s a start.”