Sir Edmund and Norgay were part of a Royal Geographical Society-Alpine Club expedition, led by Col Henry Cecil John Hunt, a siege group that included a dozen climbers, 35 Sherpa guides and 350 porters carrying 18 tons of food and equipment. Their route was the treacherous South Tor, facing Nepal.

After a series of climbs by coordinated teams to establish ever-higher camps on the icy slopes and perilous rock ledges, Tom Bourdillon and Dr Charles Evans were the first team to attempt the summit, but gave up at 28,720 feet — 315 feet from the top — beaten back by exhaustion, a storm that shrouded them in ice and oxygen-tank failures.

Sir Edmund, then 33, and Norgay, 39, made the next assault. They first established a bivouac at 27,900 feet on a rock ledge 6 feet wide and canted at a 30-degree angle. There, holding their tent against a howling gale as the temperatures plunged to 30 degrees below zero, they spent the night.

At 6.30 am on May 29, 1953, cheered by clearing skies, they began the final attack. Carrying enough oxygen for seven hours and counting on picking up two partly filled tanks left by Evans and Bourdillon, they moved out. Roped together, cutting toe-holds with their ice axes, first one man leading and then the other, they inched up a steep, knife-edged ridge southeast of the summit.

Farther up, they encountered what was later named the Hillary Step — a sheer face of rock and ice 40 feet high that Sir Edmund called “the most formidable obstacle on the ridge”. But they found a vertical crack and managed to climb it.

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