The Ministry of Defence should be stripped of its immunity from prosecution after being blamed for the deaths of three reservists on a special forces selection march, families have said.

Lance Corporal Craig Roberts, 24, and Lance Corporal Edward Maher, 31, were pronounced dead on the Welsh mountain range after suffering heatstroke on July 13 2013.

Corporal James Dunsby, 31, died at Birmingham’s Queen Elizabeth Hospital from multiple organ failure more than two weeks later.

The soldiers were part of a group of 37 reservists and 41 regular troops taking part in the 16-mile test march in the Brecon Beacons, which had a time limit of eight hours and 48 minutes.

They carried backpacks weighing up to 27kg as well as dummy rifles on the arduous exercise, which took place on one of the hottest days of the year.

Two servicemen, known only as 1A and 1B, were acquitted of negligently performing a duty by failing to take reasonable care for the health and safety of the candidates.

Judge Advocate General Jeff Blackett found that 1A, a serving captain, and 1B, a former warrant officer, had no case to answer and said the deaths were caused by failures by Joint Forces Command, part of the Ministry of Defence.

“The deaths occurred because of the systemic failures within Joint Forces Command,” he told families of the reservists.

“Of course, the system is made up of people but there have been successive people in A-Block and within the chain of command who have failed to address their minds to the real risks involved in exercising in extreme temperatures, and who have failed to ensure that those delivering the training or invigilating the test were properly trained in all aspects.

“The two defendants did the best they could in the circumstances of fewer resources than requested, a lack of even the most basic training in relation to heat illness and risk assessment and within the culture that existed at the time.”

The soldiers were on the Brecon Beacons Credit: PA

An anonymity order protects the identify of a number of people and organisations that featured in the court martial.

Judge Blackett refused an application by the media to identify A-Block, referred to only as an organisation within Joint Forces Command.

Following the deaths, the Health and Safety Executive (HSE) issued a Crown censure against Joint Forces Command.

This document says there is sufficient evidence for a realistic prospect of the organisation being convicted of a criminal offence in relation to the deaths, if it did not have immunity from prosecution.

The Crown censure, released following a freedom of information request by the Press Association, said: “The investigation revealed systemic failings in the health and safety management of test week.

“These multiple failings are not attributed to any individuals but lie within the organisational management chain. The extent of these failings was serious, falling far below the health and safety standards the law requires.”

It concluded that the failings exposed candidates on the march to preventable risk, adding: “It was reasonably practicable to have prevented the deaths.”

Bryher Dunsby, widow of Corporal James Dunsby, making a statement outside court Credit: Andrew Matthews/PA

Sarah Baldwin-Jones, of the HSE, said it was a “fundamental error” that there was still no MoD guidance on how high temperatures affect the body over a prolonged period of time, such as on endurance marches.

Temperatures had reached 26.3C from midday on the day of the march and had risen to 28.3C by 4pm.

Judge Blackett said a decision by A-Block to march candidates the following day “was indicative of the culture and lack of care within the chain of command”.

Speaking outside the court martial, Bryher Dunsby – widow of Cpl Dunsby – called directly on General Mark Carleton-Smith, head of the Army, to prioritise new guidelines relating to heat illness and endurance exercises.

“The MoD are still protected from prosecution for corporate manslaughter by Crown immunity, there is an obvious need for this in live combat, but I believe not in training in Wales,” Mrs Dunsby said.

“Without ultimate accountability or punishment from the law, there is no incentive to do the right thing.”

Clare Stevens, who has represented members of two of the reservists’ families, described 1A and 1B as “scapegoats for those at the top”.

“The MoD is immune from prosecution under health and safety legislation, so it received a Crown censure – just a recording to confirm had they not been exempt from prosecution, they would have been prosecuted,” she said.

“That is simply not good enough. Until they are held properly accountable, there is no impetus to change.”

The Army said that since 2013, heat illness prevention guidelines have been updated three times and are “embedded” in training culture.

Research into the effects of heat illness is being conducting to ensure training meets the “very highest medical standards”.

L/Cpl Roberts was originally from Penrhyn Bay in North Wales, L/Cpl Maher was from Winchester in Hampshire, and Cpl Dunsby was from Trowbridge in Wiltshire.