The number of claimants alleging systemic physical and psychological abuse in an action against British Gymnastics has more than doubled since last month to 37, and represents “the tip of the iceberg” according to the group involved.

A letter before action was sent by law firm Hausfeld to the governing body last month, initially on behalf of 17 claimants including three former Olympians, regarding abuse perpetrated by coaches.

That number has now grown significantly, and Hausfeld has said it will pursue the matter through the courts if British Gymnastics has not provided a substantive response by June 19.

The law firm had asked for a response to the letter it sent on February 25 by this Thursday. Hausfeld said British Gymnastics had asked for an extension until December 19, something the group involved in the action felt was unacceptable and was putting “current gymnasts at risk of similar serious harms”.

“We’re disappointed but not surprised that British Gymnastics have failed to meet the reasonable deadline we set,” a spokesperson for the group legal action said.

“As such they have missed a valuable opportunity to address the 17 cases of harm put to them and to commit to working with gymnasts and former gymnasts to reforming the sport through an alternative dispute resolution.

“British Gymnastics are presiding over a broken system and their attempts to ‘long grass’ our claims are indicative of that fact. Every day that they delay, former gymnasts are denied the justice they so richly deserve – and current gymnasts are at risk of similar serious harms.

“Since we issued our letter before action a further 20 gymnasts have come forward, representing the tip of the iceberg in terms of the number of gymnasts who allege they have been harmed over a 40-year period.

“We now look forward to hearing from British Gymnastics by no later than June 19, 2021.

“We’re very clear in our determination that if British Gymnastics do not put their full organisational weight behind addressing our case, then we will take the opportunity for British Gymnastics to be part of reforming the sport we love out of their hands and into the courts.”

One of the claimants, Claire Heafford, told the PA news agency last month that coming out of the club gymnastics environment was like “leaving a cult”.

“There was physical abuse, pushing and slapping,” she said.

“Despite training six hours a day we were told every day that we hadn’t done well enough, we weren’t trying hard enough, they were ashamed of us.

“These belittling, humiliating things were shouted at us on a daily basis.”

She said her experiences in gymnastics had led to feelings of worthlessness in later life.

Almost 400 submissions are being considered by the independent Whyte Review into allegations of abuse and bullying within the sport, with 39 of them so potentially serious they have been referred to the relevant statutory authorities.

An interim report by review leader Anne Whyte QC said over 90 clubs and 100 coaches had been identified among the submissions, 126 of which were provided by current and former gymnasts. She confirmed that “many” but by no means all of the allegations relate to the elite level of the sport.

The final draft of her report is expected to be published around August.

British Gymnastics interim chief executive Alastair Marks said he welcomed publication of the interim report, stressing the organisation is “fully committed” to helping the Whyte Review obtain the answers it needs.