A campaigning vegetarian duke and duchess are leading an aristocratic revolt against the department store Selfridges from within the walls of a 14th-century ancestral home in Scotland.

The Duke and Duchess of Hamilton, who maintain their position as the head of the peerage in Scotland from their 460-acre estate, Lennoxlove, near Edinburgh, have announced they will boycott the chain in protest at its continued sale of foie gras.

The duchess set out the family's position in a letter to Selfridges' chief executive Paul Kelly in which she described the force-feeding of duck and geese to make the liver pâté as a "grotesque abuse of animals". "As you must surely realise by now, long inflexible pipes are jammed down the throats of ducks and geese as many as three times a day, and several pounds of feed are forced into the animals' stomachs," she protested. "This cruel process causes the birds' livers to become diseased... Some birds have their necks torn open by the pipes, and sometimes the animals' internal organs rupture."

In her letter, which carried the Hamilton crest, the duchess pointed out that Prince Charles had banned foie gras from Royal menus. "I deeply regret to say that my husband and I will boycott Selfridges and encourage our friends and family members to do the same until you end the sale of foie gras," she wrote.

By campaigning against foie gras, the duchess and her husband – whose full name is Angus Alan Douglas Douglas-Hamilton, Duke of Hamilton and Brandon, Premier Peer of Scotland, Hereditary Keeper of Palace at Holyrood House, PC, KT, GCVO, AFC – are allying themselves in principle with members of the Animal Liberation Front, whose protests against foie gras have included throwing a brick through a restaurant window.

The chef Raymond Blanc last year disclosed he had received threatening letters for serving foie gras in his Michelin-starred restaurant, Le Manoir aux Quat'Saisons in Oxfordshire.

In the past two years retailers have resembled a row of collapsing dominoes by withdrawing their support for foie gras one by one, following peaceful protests by animal welfare groups. The duchess is a veteran of one such campaign having boycotted Jenners department store in Edinburgh in 2000. After she received 400 letters of support from members of the public, Jenners' owners, the House of Fraser group, banned foie gras last year. Its rival group Harvey Nichols removed the product following protests from the vegetarian group Viva!

None of the leading supermarket chains stock the product on welfare grounds but Selfridges has remained one of a few stores to risk the wrath of protesters. Production is banned in 15 countries, including the UK, Germany, Italy, Poland, Switzerland, Denmark and Turkey. However under the Treaty of Rome, France enshrined its right to make and export the product.

Campaigners hope the support of the ducal couple will spur other members of the aristocracy, as well as the public, to boycott Selfridges. "It's a really strong symbol," said Noemie Ventura, the foie gras campaigner at People for the Ethical Treatment of Animals (Peta). "Selfridges has a royal warrant so it's good that high-profile people like the duchess feel so strongly about foie gras that she is going to boycott it until it stops selling it."

Charles Kidd, editor of Debrett's Peerage & Baronetage, said: "After a member of the Royal Family, the best aristocrat you could get with clout would be a duke or a duchess so the foie gras campaign should be pretty pleased they've got the highest rank of the peerage."

Looking back to her campaign against Jenners, the Duchess said: "One person wrote to us saying: 'It's so good that you are speaking out because you will get reporters phoning you – and we won't." It's sad that a title gets you listened to, but it's a fact."

Selfridges made no comment.