Sir Ranulph Fiennes is to demand that Government ministers drop their attempts to repeal the ban on fox hunting, after an injured animal forced him to reverse his opinion on the subject.

The polar explorer was due to address a fringe event on Sunday night organised by the League Against Cruel Sports at the Conservative Party conference in Birmingham, during which he was expected to switch sides in the debate on hunting with hounds.

Sir Ranulph was previously a strong supporter of fox hunting and has spoken at pro-hunt rallies, where he accused politicians of using the hunting ban for political gain.

But now he was scheduled to tell Conservative politicians and activists gathered in Birmingham that fox hunting was a “brutal and insupportable self-indulgence”.

“The conflation of ‘countryside’ with ‘cruelty’ must stop. As a conservationist, I recognise the value of the Hunting Act," he was due to say.

“Hunts talk about wildlife management, but the only ‘wildlife management’ hunts do is the raising of fox cubs to be hunted or baited.

“They talk about tradition. But the so-called tradition of terrifying wild animals for pure enjoyment is now, as it always has been, a brutal and insupportable self-indulgence.”

Sir Ranulph, who was the first person to walk to the North and South Pole and cross Antarctica on foot, was expected to reveal that he changed his mind on fox hunting after discovering a fox on his farm in Cheshire that had been injured during a hunt.

““After my wife and I saw the fox’s injuries, we called the vet. We laced food with medicine and left it out for her in an attempt to prevent infection setting in from bites to her rear," he was due to say.

“Sadly, six days later, we found her curled up dead in a field shelter next to the house. She may have gone there to die because she knew it was a safe place.

“To chase a wild animal with a pack of dogs is illegal and has been for over 10 years. The Cheshire Hunt chased that fox before our eyes and she took six days to die.

“Do not believe hunters when they say the fox has a quick and painless death. Our fox’s death was slow and agonising. You try being chewed to death by hounds.”

It comes as Conservative ministers pressed ahead with their 2015 manifesto pledge to give Parliament a free vote on repealing the hunting ban.

Andrea Leadsom, the Secretary of State for Environment, Food and Rural Affairs, previously made support for fox hunting a core part of her failed campaign to become Conservative leader.