It took around 30 hours for emergency teams to be able to reach Philip Goodeve-Docker's team and airlift them to safety but Mr Goodeve-Docker died before their arrival.
The London events manager was on the unsupported crossing with experienced expedition leader Roan Hackney and Andy Norman, a former IT professional, who both remain in a "critical condition" in hospital.
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In a wide-ranging Peston on Sunday interview, he said Parliament security needs reviewing and the PM's counter-terror strategy is flawed.
The terror attack carried out by Khalid Masood at Westminster that left four people dead lasted less than two minutes say police.
Two knives were found at the scene in Islington, North London, and the suspects fled on foot before being arrested.