Amanda Feilding – the future Countess of Wemyss and March – was a notable eccentric on London’s bohemian social scene in the late 1960s and 1970s, said Tatler. One night in December 1970, when she was 27, she arrived at a party draped in a Moroccan kaftan, with her beloved pet pigeon Birdie perched on a shoulder; on her head, a silk turban; and in her forehead, a 4cm hole that she had bored herself earlier that day, using a pedal-operated dentist’s drill.

She was an advocate of trepanning, an ancient practice that she thought would improve blood flow to the brain. She had prepared carefully for the surgery (even bringing a spare drill, which she needed as the first broke) and filmed it, for use in a documentary. “Heartbeat in the Brain” was so gruesome that at a screening, a reviewer reported that people fainted, “dropping off their seats like ripe plums”.

Feilding was ridiculed as the Crackpot Countess and Lady Mindbender – yet her legacy is a serious one, said The Daily Telegraph. When she was 22, someone spiked her drink with LSD, giving her a massive overdose from which she took months to recover. Nevertheless, she came to believe that psychedelics had potential mental health benefits, and in the 1990s she launched The Beckley Foundation, to drive serious research into the area. “I am happy to be proved wrong,” she said. “What I want to do is know.”

She was born in 1943, and brought up at Beckley Park, a triple-moated Tudor lodge in Oxfordshire. Her parents were unconventional and so was her upbringing. “We ran wild,” she once said. “We were like the Mitfords without the politics.” She left school at 16, went travelling and, for a period, made money selling hand-coloured prints on London‘s Portobello Road. By the mid 1960s, she and her friends had discovered that small doses of LSD could make them feel “sparkly” and better able to concentrate, rather than high.

Over time, she “cannily” stopped championing trepanning, which just made her seem “batty”, and instead focused her efforts on psychedelics. In 2008, she co-founded a research programme at Imperial College, with Professor David Nutt; and in 2016, a Beckley/Imperial study published in the journal The Lancet Psychiatry found the first evidence that psilocybin, the LSD-like ingredient in magic mushrooms, could, when used in conjunction with psychotherapy, be effective for treatment-resistant depression. She is survived by her husband, the 13th Earl of Wemyss and 9th Earl of March, and her two sons.