Wales international Josh Navidi and former England flanker James Haskell are among rugby figures calling for reform to protect players' wellbeing.

In an open letter to World Rugby, the group says more should also be done to inform parents about the risk of brain injury from repeated head knocks.

World Rugby say many of the proposals were already being actioned.

"The welfare of the global rugby family is, and has always been, World Rugby's priority. We take our responsibility very seriously and care deeply about our past, present and future players," said the sport's governing body in a statement.

"That is why we ensure that players are at the heart of our discussions through International Rugby Players, and that is why we value and welcome constructive debate, respect opinions and listen to suggestions that advance welfare.

"We are progressive, which is why as scientific and medical knowledge and societal understanding continues to evolve, rugby evolves with it. We are always guided by medical and scientific consensus to inform our concussion education, prevention and management strategies.

"Clearly these members of our rugby family love the game and want it to be the best it can be. We do too.

"We are encouraged that the group are championing a number of initiatives that are already operational or being considered and we are open to constructive discussions with them regarding their proposals."

In December 2020, nine retired rugby professionals, most of them diagnosed with early onset dementia, began legal action against World Rugby alleging negligence after repetitive head injuries during their careers.

A group of more than 20 players, coaches and doctors, are demanding immediate changes to the way rugby union is played and how laws are enforced, in order to prevent repeated concussion incidents and damaging brain injuries.

Former Canada international Jamie Cudmore, who has had his own considerable difficulties with concussion and former England forward Haskell are among Progressive Rugby's founders.

Haskell said the intensity of physically demanding training sessions should be modified and that players should only be allowed to return to play after concussion when properly assessed and ready he added.

In December 2020, former Wales international Alix Popham was diagnosed with early onset dementia.

The diagnosis pushed him and seven other former rugby union players to start a claim against the game's authorities for negligence.

Since then Progressive Rugby say the lawsuit has grown to more than 150 former players.

Popham said lessons should have been learned from other sports such as American football and Australian Rules football, where action has already been taken.

The group warned that, without immediate changes, the issue was an existential threat to the future of rugby union.

The group are lobbying for a rugby union concussion database, health passports, involvement of independent brain experts alongside sports scientists and limiting the number of substitutions among other things.

"We all love the game of rugby, and want to see it continue in the long-term," said Progressive Rugby's Dr Barry O'Driscoll, a former World Rugby medical advisor.

"However, the game as it is, is broken, with many more players likely to end up with neurological impairments in the future."

World Rugby chairman and former England captain Sir Bill Beaumont wrote an open letter in response to the lawsuit in December 2020, in which he said as "the science continues to evolve" rugby will "evolve with it".

In a statement, Progressive Rugby say they support the physicality of rugby, including tackling in school rugby, but believe "much more can be done to protect current players and future generations".

Progressive Rugby's open letter to World Rugby is signed by Navidi, Haskell, Popham and Cudmore, as well as former players Jonathan Davies, Steve Thompson, Rory Lamont, Tim Stimpson, Kyran Bracken, Geoff Old, John Shaw, Emyr Lewis, Steve Hanley, Catherine Spence, Paul Wallace and Inoke Afeaki.

Teachers from rugby schools Dan Harrison, Chris Hattam and Marc Batten, and medical professionals Dr Rohit Kulkarni, Dr O'Driscoll, Prof John Fairclough and Prof Bill Ribbans have also signed the letter.

Former Welsh Rugby Union chief executive David Moffett, former Ospreys coach Sean Holley, referee coach Antony Kozlowski, referee James Jones and the Chair for All-Party Parliamentary Group for Acquired Brain Injury, Chris Bryant, complete the signatories.