It is touch and go whether Sir Ranulph Fiennes, who turned 63 last week, will start his attempt to climb the north face of the Eiger this week.

“It was snowing until a little while ago,” Fiennes said from his hotel yesterday. “That means there will be deep snow sitting on all the steep slopes waiting to avalanche.”

Falling rocks and snow are one of the great dangers of the climb, which Fiennes is determined to do to raise money for the Marie Curie Cancer Care charity. But forecasters in Switzerland are predicting a window of fine weather beginning tomorrow.

“Generally Monday to Friday seems to be looking good,” said Fiennes. “But they are not happy about Thursday.”

It makes the decision on whether to climb tricky. The best climbers can complete the face in a day or two, given fine weather. But the team guiding Fiennes, an explorer rather than rock-climbing specialist, must allow four or five days.

“Hopefully we will start on Monday or Tuesday,” said Kenton Cool, the British mountain guide who will make the decision. “But everything depends on the weather.

“Ran is not the fastest climber and we need a long window. But if Thursday is looking good, we might go. It’s in the balance.”

Cool is one of Britain’s leading alpinists and has climbed Everest three times. In 2005 Fiennes got within 300 metres of the summit of Everest, which he climbed to raise money for Great Ormond Children’s hospital. His efforts brought in £2m.

But the Eiger is an entirely different challenge. While Everest is a test of altitude endurance, the north face of the “Ogre” is 6,000ft of steep rock, ice and snow.

“It would be stupid to be 4,000ft up the face when bad weather strikes,” he said.

Fiennes has a poor head for heights, and plans not to look down. Nor has he read The White Spider, the gripping account by Heinrich Harrer of how the north face was finally conquered in 1938 after numerous deaths. “I was advised not to read it,” he said.

This weekend Fiennes sounded remarkably calm. “I just sit here waiting,” he said.

The man under pressure is Cool. “It’s a tough one,” he said. “If we don’t go, it will probably be fine and we’ll be kicking ourselves. But if we do go, the s*** will more than likely hit the fan.”

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