The parents of a teenager who died in sweltering heat on a trek in Morocco have criticised the company that organised the trip.

Ken Boon, father of 17-year-old Samuel, said they would never have allowed him to go on the school trip in July 2012 if they had known about the arrangements for emergency care put in place by World Challenge.

"If we had known that in an emergency there would have been no helicopter, no ambulance, no medic, in fact the best emergency response available was a minibus with no medical assistance, we would never have allowed Sam to go," Boon said after the conclusion of an inquest into his son's death. "In fact I don't think there is any school in the country that would go."

The assistant coroner for south London, Selena Lynch, returned a finding of misadventure.

The inquest in Bromley, south-east London, heard that Samuel collapsed on 17 July 2012 while trekking in the foothills of the High Atlas mountains in temperatures of 39C.

A local guide was asked to get an ambulance but more than an hour later a minibus arrived to transport the teenager to a medical facility, the inquest was told.

"Plans for evacuation relied almost entirely upon local agents to find and obtain appropriate facilities," Lynch said. "They were appointed without their qualifications being checked or references obtained, and were not given any formal training.

"There were no arrangements in place for an ambulance with medical equipment and/or personnel to be provided in an emergency, and the facilities at local medical centres had not been assessed."

The inquest heard that Samuel, who was 6ft 2ins and weighed 20 stone, had been prescribed medication for bed-wetting. His mother, Karen Boon, said her son had a repeat prescription for the drug DesmoMelt, which he had taken with him to Morocco.

Lynch said the cause of death was either exertional heatstroke and/or hyponatremia – a condition where salt levels are reduced in the blood – caused by excessive intake and/or retention of water.

She said the teenager may have taken the medication in the recent past which could possibly have caused or contributed to hyponatremia, but it was not possible to determine whether he or it did so.

"The cause of Samuel's death was contributed to by his obesity and lack of fitness and acclimatisation," Lynch said. "These risk factors and his tiredness and obvious difficulty in keeping up with the trek were not fully recognised by the leaders, who were inexperienced and lacking in local knowledge."

She added: "Samuel and his parents were given inadequate and misleading information about the level of fitness required or the risks involved in the trip and how they would be managed. He was not adequately assessed as to his physical ability to participate."

She said Samuel collapsed at around 3.30pm and "quickly became unconscious". Leaders gave first aid and attempted to cool him, she said.

"Samuel was carried to the road where it was noted that his breathing had ceased. Cardiopulmonary resuscitation (CPR) was performed by the leaders and Samuel was placed in the aisle of the minibus. By this time it was probable that Samuel's life could not have been saved even with advanced medical treatment."

Once in the minibus it was not possible to perform further CPR within the confines of the aisle, she said, and Samuel died during the 25-minute journey to the medical centre at Marigha.

The inquest has heard that 11 pupils from the Bexley Business Academy were on the trip, which was cut short after the death. Lynch said she would send a report to the Department for Education. "In doing so, I recognise that significant changes have been made by World Challenge since Samuel's death," she said.

Matt Eastlake, managing director of World Challenge, said after the inquest: "Samuel Boon's death was an absolute tragedy and our deepest sympathies remain with his family and friends. World Challenge's highest priority is the safety of its participants and, as the coroner noted, we have introduced a number of new measures since Samuel's death, especially in terms of monitoring participant fitness.

"We will take time to reflect on the coroner's findings and give serious consideration to any change or development where we feel appropriate which will improve safety further."

Sam Elms, chief executive of Bexley Business Academy, said: "If we had been made aware from the beginning that in the event of an emergency the best that we could hope for was a local minibus with not even the most basic medical facilities or equipment on board and no trained medic to save lives, we would not as an academy have signed off on the trip.

"I urge schools and academies involved in World Challenge expeditions to examine all aspects of the organisation of the trip, particularly the choice of expedition leader, in-country staff and evacuation procedures. The academy community is devastated by the loss of Sam Boon and will never be the same again."

She said she wanted to pay tribute to the students on the expedition and her staff who had done "everything possible" in an attempt to save Samuel's life.