An army training march on a hot summer’s day in which a soldier collapsed and died should not have gone ahead, a heat expert has told an inquest.

The expert said a key piece of equipment used in the military to assess heat during exercise was “erroneously” placed in the shade of a building and its readings could not be relied on.

Cpl Joshua Hoole, 26, collapsed during an annual fitness test in south Wales on the morning of 19 July 2016.

Three years earlier, three army reservists sustained fatal heat illness in an SAS selection march close to the same spot in the Brecon Beacons.

Hoole, of Ecclefechan, southern Scotland, was a quarter of a mile from the end of the eight-mile (13km) cross-country course, carrying 25kg (55lb).

From leading the march, he rapidly fell back through the pack, complaining of cramps, before collapsing at 8.52am. He was pronounced dead less than an hour later.

Eighteen out of a total of 41 soldiers dropped out, collapsed or were withdrawn by the course directing staff on the day.

On Friday, Prof George Havenith, a heat stress and heat strain expert from Loughborough University, told the inquest in Birmingham that the wet bulb globe temperature device used to measure heat produced an “erroneous” result because it was in the shade of a gym building.

“I was convinced that any point taken before 10am was definitely an incorrect measurement,” he said.

Asked on a balance of probabilities whether the march should have gone ahead, Havenith said it should not.

Asked if Hoole would be alive if the exercise had not been run or had been stopped half an hour before he collapsed, Havenith replied: “Yes.”

Witnesses said another soldier, L/Cpl George Knight, blacked out and fell into a hedge about an hour before Hoole became ill.

Questioned about Knight’s collapse, Col Christopher Wright, a military doctor in emergency medicine, said: “I had come to the conclusion that it should have been treated as a suspected heat injury.”

Asked by the senior coroner, Louise Hunt, what he would have expected to have happened if a potential heat injury had been identified, Wright said: “The exercise has to stop.” The fitness test continued, however, and more soldiers dropped out or were withdrawn.

Hunt also presided over the 2015 inquest into the deaths of the three men after the SAS march. At the end of that hearing, she concluded there was a “catalogue of very serious mistakes” by many people involved in the planning and execution of the exercise, and called for changes to how marches were organised on hot days.

The inquest continues.