They’ve been dubbed the champagne swampies – beautiful, aristocratic greenies who’ll happily chain themselves to trees before that motorway slices through the estate: Zac Goldsmith, David de Rothschild, Tamsin Omond.

Champion of the eco-toffs, however, has to be Tracy Worcester. Her secondary-modern first name belies the fact that she is married to the Marquess of Worcester, son of the Duke of Beaufort, who will in due course inherit the 52,000-acre Badminton estate. She splits her time between a cottage there and her Belgravia townhouse, a paean to shabby chic, where she is now passing mugs of coffee beneath signed Francis Bacon prints. Is the Maserati outside hers?

“Oh my God!” she says. “Of course I don’t have a f****** Maserati!” She bounds over to the window and points out a bicycle. “That is what gives me my greatest happiness, cycling through London,” she says. “Particularly in the rain.”

The marchioness is posh, albeit in a carelessly beautiful, untweedy way. She is wearing cast-offs: jewelled slippers from granny and secondhand clothes (she loves Oxfam), and although she’s scraping 50, still goes for black kohled eyes and artistically messy hair, very much the fading bohemian model. Her chief delight is to be with her children, Bobby, 20, Bella, 17, and Xan (short for Alexander), 13. They are all away at university or school, which is odd since the marchioness swears she cannot stand such institutions. “They all wanted to go to boarding school,” she claims. “There was no Rudolf Steiner school [her preferred option] in the village.”

Schooling is just one of the many drums that she bangs. She is a dyed-in-the-wool antiglobalisation nut and forthright in indicating how people should shake up their lives. But would she give it all up herself? She doesn’t need to work. “Harry pays all the bills,” she says simply. This leaves her time for pressing her ecological crusade on others. Such as a TV documentary she’s just made about commercial pig farming.

It took her four years. There is some standard footage of distressed pigs heaving around farrowing crates and ghastly shots of people throwing boxes onto the heads of more distressed pigs, plus some unsavoury information detailing what happens to pig excrement on giant commercial farms (it ends up on some people’s land, apparently). She takes meat processing companies to task for animal cruelty, pollution and human rights abuses. Her film is forthright, worthy and earnest. It is also somewhat weak on actual evidence.

“I’ve got the evidence,” she says indignantly, when I point this out. “It’s in a giant lever-arch file. It’s just that the film is 77 minutes long and we couldn’t put it all in.”

Is she an investigative journalist manqué? She smiles, a private smile as if annoyed by the implication that I doubt her professionalism. “I could have done that,” she says. “But I have come from the angle of ecology. My area of interest and knowledge is the system itself. I don’t know how free journalists feel in their ability to report the truth. My work is about the truth.”

What does she hope to achieve in her film? “I would like to show what is the true cost of meat on the super-market shelf. And so people will say, I don’t want to touch that, because I don’t want to be part of a system that creates that suffering.”

Well, everyone knows that cheap meat is probably unhappy meat. And I suppose if your husband is up for a fortune of many millions, you could probably afford to bathe in happy pig milk every night. (Or, as her fellow champagne swampy Rosie Boycott does, let them play football.) But many viewers might take a dim view of Lady Worcester exhorting them thus. The timing isn’t exactly right, is it? She smiles sadly and twists her elegant fingers around.

“If you get rid of your small-scale farms, the big producers will have to start producing meat in the ecological way we all want it. Which will eventually cost us all more,” she says. “It’s not an awful lot more expensive anyway.” She sighs, as if affronted. “It’s just information – take it or leave it.”

How does she see herself? “Pretty much free to do what I want to do. Because I have enough money.” So why does she insist on trooping off to film dodgy practices with pigs? “Maybe a psychoanalyst would give a trillion reasons why I fight for justice.”

The marchioness has always been wealthy. Her father, Peter Ward, was brother of the Earl of Dudley.

Her mother is from the Baring family. She admits she had a challenging upbringing: Ma and Pa lived in London while she, her actress sister Rachel (who was in The Thorn Birds) and their younger brother Alexander were brought up in the country by a nanny. She attended no fewer than 11 schools. Her eventual expulsion for slapping a teacher for barring classmates from using a telephone may be the key to her elegant truculence.

“Certainly, the rules of a boarding school are absurd and ridiculous and I couldn’t stomach them,” she says.

“I want people to be treated like intelligent human beings and for their choices to be respected. Therefore I want local, powerful governance. I am someone who advocates changing the rules from the ruling system, which destroys small and puts all of the might into giant corporations. I don’t want to live in a world which is ruled by incredibly wealthy companies.”

What’s the alternative – a medieval feudal system? The private smile again. The marchioness is thinking I see her as some sort of ancient landowner, giving largesse to the populace. I wasn’t actually but, now we’re on the subject, would she consider carving up the Badminton estate and giving it to the small farmers? Again, a sigh. This is clearly an old chestnut. “You are talking to me. You are not talking to Harry Worcester. Badminton belongs to Harry Worcester. My say is nothing. What my son does is completely different because he has had two people advising him.”

What is your advice? “He knows my views.” Which are what? “What I would like is that he is part of a political and local movement saying stop bankrupting local farmers. And not part of a system which will inevitably hit the wall.” So redistributing the Badminton wealth is not the answer? “It would hit the wall instantaneously. I tried. I put my money where my mouth was and employed people to work on my market garden. But I couldn’t do it.

“There is a third way,” she insists. “It’s not feudalism, or giant corporate feudalism, but small-scale and protected by the government. Capitalism has been eroded by big business and I think it is extremely dangerous.”

What about being branded a champagne swampy? “For me it just reveals the shallowness of the media and who they pick up on,” says Tracy Worcester crisply. That’s put me in my place.

True Stories: Pig Business, part of the Great British Food Fight season, is on More4 on February 3 at 10pm

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