The 25-year-old step-daughter of Baroness Mallalieu, the hunt-supporting Labour peer, was standing on a wall at Hyde Park corner with the fox draped around her shoulders.
"It was my grandmother's," she said, "so if I didn't wear it it would mean the fox's death had served no purpose. Generally, people have liked it, but I did have a woman come up to me in the park and call me a filthy slag."
Ms Cassell, a member of the Bicester Hunt, and her friends were anxious to get across the need for fox-hunting as a necessary part of country life.
"What about the employment it provides?" she asked. "Without it, thousands of people's jobs would be wiped out overnight. There are farriers who earn only pounds 7,000 a year but get a tied cottage. What would happen to them?"
Her friend, Nick Morrey, a dandy 26-year-old wearing a Bertie Wooster- style suit, cravat and python-skin shoes, agreed. "We are sick of being lectured on the countryside by people who know nothing about it," he said. "People who hunt are also people who care for and look after the countryside. What would happen to the horses, the dogs and the people who work for hunts?"
It was clear, however, that Mr Morrey did not rely on the hunt for a living. When asked what he did, he sniggered and replied: "Ah, nothing really."
All around them the marchers flowed like lava in their tens of thousands. It was a gathering of the most dreadful old buffers and young fogeys, of upper class twits of the loudest kind, where appalling dress sense was de rigeur and class-consciousness was compulsory.
It was also a gathering that could not be ignored because of its sheer size and conviction. And it was an occasion that will stay in the memory for its peacefulness and warm atmosphere. There was something mildly amusing about country folk taking their litter home with them.
Brass and pipe bands led the masses through Piccadilly and past supporters on the balconies of the most exclusive clubs. Huntsmen blew into their horns, eliciting huge cheers from their followers.
Huntspeople and farmers and countryside employees from Scotland, Northern Ireland, Wales and England streamed along the route for five hours. And all the time, only a handful of anti-hunt protesters dared shout at them.
Others, however, had a cheekier idea. They hijacked the frequency on which the Countryside Alliance's "March FM" was broadcasting for the day and drowned out the signal with their own in many parts of London.
Calling themselves the Hunt Saboteurs Broadcasting Corporation, the hijackers replaced the pro-hunting station with music from a DJ who, in the best traditions of the countryside, shouted: "Fuck off our land. Now!"