A senior coroner hearing the inquest of a soldier who died while taking part in a fitness test on a searingly hot day in the Brecon Beacons has strongly criticised the army for not learning from failings exposed when three men suffered fatal heat illness during an SAS trial.

Cpl Joshua Hoole, 26, died near the end of an eight-mile course in south Wales in July 2016, three years after three army reservists collapsed in the same area in the SAS march.

Giving her conclusions, the coroner Louise Hunt said a string of “very serious failings” had meant the annual fitness test (AFT) in which Hoole was taking part was not safe. She said she believed the march should not have gone ahead because of the heat and concluded that the safety assessment carried out was not fit for purpose.

Hunt added: “It leaves me very worried about the army’s ability to learn from previous mistakes. It’s a matter of grave concern. I want to give a message to the army that they need to think about how to learn. Quite simply, something has to change.”

Hunt’s comments were echoed by Hoole’s father, Phillip Hoole, who said the Ministry of Defence had failed to make meaningful changes since the SAS tragedy and accused it of “systemic organisational failure”. He said he intended to launch a civil action against the MoD for corporate manslaughter and called for the police to investigate.

“Many promises were made and undertakings given to implement change,” Hoole said. “It is my belief that the MoD failed in its duty of care to implement any meaningful changes.”

He was particularly angry at a report on his son’s death carried out by the Defence Safety Authority that he said had sought to rule out a link between Hoole’s death and heat. He claimed the report contained lies and inaccuracies.

Bryher Dunsby, whose husband James was one of the three who died in the SAS test, said she believed there had been an attempt to cover up what happened to Hoole.

She said: “The MoD are willing to defend themselves at all costs, regardless of truth or justice for the individual who has died and their families.”

Dunsby said she knew that special forces had updated and modernised their training and attitude to heat. “However, this clearly has not been transferred to the rest of the British army. This needs to happen as a priority: more of our service personnel will die in training if it is not addressed.”

Giving a narrative conclusion, Hunt highlighted that of the 41 corporals and lance corporals taking part in the AFT only 24 completed it, with many complaining of the heat being magnified because it was held in by the hedges lining the lanes in which they were moving with full pack and rifle. One said it felt hotter than Afghanistan.

The coroner said another soldier, who collapsed before Hoole died, should have been recognised as a casualty of the heat – which ought to have led to the AFT being halted. In fact, those in charge of the AFT thought he had an ankle injury. The soldier was told later in hospital he could have died if he had not stopped.

Hunt oversaw the SAS inquest in 2015 and issued a report intended to prevent further deaths, specifically raising concerns about issues such as the lack of awareness about heat and risk assessments.

She said: “The failure of the army to learn from previous mistakes is a very concerning matter for me.” She said she would write another report on preventing further deaths to the defence secretary.

The coroner said the AFT should not have gone ahead at all because when the trial began at about 7am the temperature would have been above 20C – the point at which such exercises should not take place.

Hunt concluded that “heat stress” was one of a number of factors that led to Hoole’s death, although she said it was not the sole factor and he also had an underlying heart condition.

Brig Christopher Coles expressed regret but did not offer an apology to Hoole’s family. He said: “The MoD has acknowledged that aspects of the policy in place which governed the training Cpl Hoole was undertaking could have been better and was in areas inconsistent. While much work has already been done to address this, we will seek to ensure it is refined and improved to help ensure a tragedy like Cpl Hoole’s death is not repeated.”