A canoe race that proved too tough for Sir Steve Redgrave will be tackled by the Clarendon School caretaker and a former pupil this Easter Saturday.

The annual 125-mile race from Devizes to Westminster is considered to be one of the world’s toughest endurance challenges and Sir Steve was one of four Olympians who failed to finish in 2012.

Clarendon School’s site manager, Dave Monk, 55, and 21-year-old former pupil Tom Barnett-Salter, who has autism, are taking on the gruelling challenge on behalf of charity Seeing Dogs Alliance. The pair hopes to complete the race in less than 24 hours.

Mr Monk said: “We’re just normal people, not athletes or marines.

“It’s going to be a huge physical exertion. There’s no sleep or much chance of a rest for 24 hours.”

The race has been held annually every Easter weekend since 1948, beginning in Devizes, winding along the Thames through Teddington before the final section down the river’s tidal portion to Westminster. About a third of the entrants fail to finish each year.

Mr Monk hopes to raise £1,000 for the charity and insists that he and Tom are undaunted by the enormity of the task ahead of them.

He said: “We’re always talking to each other as we go along, keeping the encouragement up as the going gets tough.

“We paddle every week, whatever the weather. We’ve been out in snow, sleet and rain, so we’re definitely not fair-weather paddlers.”