A Nepalese adventurer says he has achieved a feat by climbing all the world’s 14 highest mountains in just over six months, beating the existing speed record by more than seven years.

Nirmal “Nims” Purja, a 36-year-old former soldier in the British special forces, had set himself what was widely regarded as the hardest challenge in modern-day mountaineering: scaling every peak above the so-called “death zone” altitude of 8,000m in no more than seven months.

His “14/7” mission, also dubbed “Project Possible”, took him from Annapurna on 23 April to Shishapangma, in the Himalayas, on Tuesday morning UK time.

Along the way he scaled K2 in July and Everest in May – where he took the now infamous “traffic jam” photograph of crowds snaking up the ridge to the summit, sparking a worldwide debate about the numbers of climbers attempting the world’s tallest mountain.

Mr Purja already held three Guinness World Records for the fastest consecutive summits of Everest, Lhotse and Makalu in five days, the fastest time from the summit of Everest to the summit of Lhotse, and he was the first person to summit Everest twice, Lhotse once and Makalu once, in the same season.

His time of six months and six days smashes the existing record for the tallest 14 mountains, set at seven years and 10 months by the South Korean climber Kim Chang-ho.

In a statement, Mr Purja said it had been a “gruelling” six months, but that he was “overwhelmed and incredibly proud” to have completed the challenge.

“I could not have made it happen without the unending support of my friends and family who have been in my heart this entire time. We started with nothing, but look how far we’ve come,” he said.

Mr Purja served in the British military for 16 years, including 10 in the special forces, and said he was the first Gurkha to climb Everest while serving. The Queen awarded him an MBE in 2018 for his achievement in extreme high-altitude mountaineering.

His adventures have also been marked by a series of dramatic rescues, including in 2016 when he broke mountaineering conventions to rescue a climber left in the Everest “death zone”, bringing her down from 8,450m to safety alone. She is alive and well, living with her family in India.

And he briefly paused his 14/7 challenge almost as soon as it had begun to help rescue a fellow climber while descending Annapurna in April. Mr Purja and his team went back up the mountain to bring oxygen to an accomplished mountaineer who had been stranded alone for more than 36 hours, taking him down to camp where he was then helicopter lifted to hospital in critical condition.

Mr Purja’s team said that in the course of completing his main 14/7 objective, he had achieved another six world records, including the most 8,000m-plus mountains scaled in both a spring and summer season. He shaved his own record for the fastest consecutive summits of Everest, Lhotse and Makalu down to just 48 hours.

Mr Purja may be due a well-earned break – but he isn’t taking much time off to recover. He plans to scale Nepal’s 6,800m Ama Dablam peak to plant a poppy for Remembrance Day on 11 November.

He paid tribute to the support team that helped him to achieve his record, saying the challenge was “never just about me”. During the mission, one of his Sherpa guides, Mingma David, was credited with becoming the youngest person on Earth to have scaled all the 14 tallest mountains.