THE deaths of three reservists, including one from Wiltshire, on an SAS test march in "heatwave" conditions on the Brecon Beacons is an "absolutely tragic case and we will learn from it", the Prime Minister has said.

David Cameron told MPs during Prime Minister's Questions today: "I'm sure I speak for the whole House and indeed the whole country when I say our hearts go out to the families of reservists James Dunsby, Craig Roberts and Edward Maher."

His comments came as Conservative Steve Brine (Winchester), the constituency MP of Lance Corporal Maher raised the issue in the Commons.

The MP for Winchester said: "Yesterday a coroner said their deaths were the result of a series of gross failures and a catalogue of very serious mistakes by those involved in planning and running the exercise.

"Now obviously nothing can turn the clock back for those families, but would the Prime Minister ensure the army service inquiry which will now get under way does everything it can, while recognising of course that we continue to train the best armed forces in the world, to bring whatever changes are needed to prevent this ever happening again and see those responsible are held to account."

Mr Cameron said there was a need to examine the coroner's conclusions "very, very carefully and make sure that this can't possibly happen again".

He told MPs: "Having seen at first hand some of the extraordinary things that our special forces do and the bravery of people that volunteer to join and the training they do, I know how vital this is, but it's an absolutely tragic case.

"I understand the MoD has accepted the failures identified by the coroner and has apologised for these, I also understand a number of changes have already been made to this particular exercise, but we now need to study the coroner's conclusions very, very carefully and make sure that this can't possibly happen again.

"And I know the Army will also hold its own service inquiry as soon as all the civil investigations have been completed.

"It's an absolutely tragic case and we will learn from it."

The Army earlier said it was "truly sorry" after being criticised by a coroner for a catalogue of blunders which led to three deaths on an SAS test march.

An inquest into the heat-related collapse of reservists James Dunsby, 31, who was a reservist with Swindon-based A Squadron The Royal Yeomanry, Edward Maher and Craig Roberts concluded they would have survived if commanders had followed Ministry of Defence guidelines.

Narrative verdicts recorded by Birmingham coroner Louise Hunt also found that delays in providing medical help to the men amounted to neglect.

David Dunsby, 58, father of Cpl Dunsby, said action should be taken against those responsible for the failings.

"Those guys all need to be come in to order and they need to face some accountability," he told the BBC.

"What form of punishment, I just don't know, I just know they have to be made accountable."

"It shouldn't end here. Three young lads died, one of them was my son, but at the end of the day it could have been probably a lot more... were the Army lucky? Yes they probably were.

"I'd like to think that whatever happened that day, the Army benefit from it because we don't want it [to] happen again.”

Unlike many of the 34 other reservists taking part in the SAS "test week" march, the three who died all had experience of serving in hot climates.

Cpl Dunsby joined the Royal Tasmania Regiment aged 18 and subsequently enlisted with the Territorial Army in the UK. He had completed two six-month tours of Afghanistan by 2009 and was attempting selection into 21 SAS(R) after working as a supply teacher and an academic.

Cpl Dunsby died at Birmingham's Queen Elizabeth Hospital from multiple organ failure more than two weeks after the march.

In an interview with ITV News at the site where his son died, Mr Dunsby said: "The system failed and that's what killed my son.

"There should be somebody there to help them and we know on the day there wasn't. That system let me down as a father and let my son down."

Claiming the Army was fortunate that more soldiers had not died, Mr Dunsby added: "Nothing can bring James back but we need to make sure that there are things in place that will protect all the other soldiers who will be doing the same thing.

"I don't blame any particular person, I blame the system and the system failed."

Mr Dunsby described the events of two years ago as being "like a domino effect" which the emergency services could not cope with.

"The Army medical staff here couldn't cope," he said. "It was just too big. They were lucky it wasn't more than just the three. It could've been six or seven."

In a statement read to the inquest by his barrister on June 25, Mr Dunsby claimed "misinformation" supplied to him shortly after his son's collapse had given his family hope that he was not alone for very long before being treated.

His statement added: "I now know that this was a complete fabrication and that he was on the hill for 90 minutes before any help got to him."