The Ministry of Defence has named one of the two servicemen who died during a training exercise in the Brecon Beacons, after reportedly succumbing to exhaustion on the hottest day of the year on Saturday.

Lance Corporal Craig Roberts and his colleague were believed to have been taking part in the selection process for the TA section of the SAS when they collapsed. A third man is in a serious condition in hospital.

The MoD is working with Dyfed Powys Police to investigate what happened, and released a statement today which said: “It is with great sadness that the Ministry of Defence can confirm the death of L/Cpl Craig Roberts and another Army reserve soldier during a training exercise in the Brecon Beacons at the weekend.

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“Our thoughts are with their families and friends at this difficult time.

”The families of the soldiers have requested that their privacy is respected at this difficult time."

The two servicemen are thought to have died in a challenging training regime near the Storey Arms Centre in Brecon Beacons, amid some of the hottest weather of 2013 with temperatures as high as 29.5C. The Associated Press quoted an unnamed source who said: “It is a case of the people succumbing to being affected by the training that they were doing.”

David Davies, the Conservative MP for Monmouth, said he expected an investigation in wake of the incident. Speaking on BBC News he said: “It’s a terrible tragedy and I’m sure the Army will hold a full investigation and be doing absolutely everything to find out what went wrong and prevent that from happening again.”

The Brecon Beacons is one of several locations used by the military for training exercises. The area’s rugged and sprawling terrain helps prepare soldiers for warfare and is frequently used by elite forces personnel like the SAS. But its jagged topography can prove dangerous even to the most hardened soldiers.

Major Alan Davies, who was involved in contingency planning during the first Gulf War, told the BBC that it remains one of the most testing areas in the country. “On one end of the spectrum you have cadets being taken for mountain walking and at the other end of the spectrum the SAS use it,” he said. He added that the three men may have been carrying very heavy equipment and working to a deadline, which meant they would have been pushing themselves very hard. He added: “Nobody should jump to any conclusions here about what may have caused this, but obviously we all know that, for example, people who take part in marathons run a small risk of dying of heat stroke and all sorts of other things, and the British Army does train its soldiers very very hard indeed.

“The training is there for a purpose, and it is arduous training at any level, and sometimes things tragically go wrong.”

Earlier this year an Army captain was found dead on a snow-covered Corn Du mountain. Rob Carnegie is thought to have been taking part in a gruelling march in freezing conditions as part of a selection process for the Special Forces regiment, when he collapsed and died.

Last night news of the deaths was met with shock in the nearby town of Brecon, which is home to The Infantry Battle School. Brecon’s Mayor and Powys county councillor Matthew Dorrance said: “It’s incredibly sad for the friends and family of the people who have lost their lives and our thoughts are with the person who is injured.

“In one way we’ve been blessed with the weather but for people working in this heat, they’re tough conditions.”

A MoD spokesman said: “The MoD can confirm that it is working with Dyfed Powys Police to investigate an incident during a training exercise on the Brecon Beacons on Saturday in which two members of military personnel died.”