The guests at my brother-in-law Rick’s 70th birthday lunch party were distinguished, silver-haired, well heeled. Long before Rick rescued the Rothschild’s giraffe from extinction, and did so many other things for wildlife conservation in Africa, I remember him and his friends in the 1970s. The chap sitting opposite me at table, now big in IT, had once been a hard-core hippie with heavy-lidded eyes like the stoned rabbit in Magic Roundabout. A coffee baron, now discussing ‘aromatic compounds’, once wore a headband, blue-tinted shades and hair down to his bum, and a man who is today a company chairman I picture still in his Afghan fur-trimmed coat, going barefoot. They were once like characters out of a Giles cartoon, or the Camberwell carrot scene in Withnail & I. As a boy I adored being with this crowd on my exeats from prep school, listening to Led Zeppelin and reading the Fabulous Furry Freak Brothers.

Rick and my sister Bryony were married in the village of Iddesleigh near our Devon farm. A psychedelic congregation of hippies descended on the tiny St James’ church. My brother Kim appeared in a massive Afro and flares and did a pimp roll up the aisle. At the reception in the Duke of York Inn, my grandpa Reginald, a veteran of two wars and a life in India, gave a wonderful speech. I flirted with women in high-cut boots and low-slung pants. After several days of partying in Iddesleigh and at home on the farm, the freaks dispersed. What a sight they must have been. Rick and Bryony took off for America.

A few days after all the guests had gone, my mother was in the garden and my semi-retired old dad, CMG, OBE, was mucking out a cattle byre. In those days we had a hill farm in sight of Dartmoor with an ancient thatched Devon longhouse with cob and granite walls. My mother noticed a convoy of cars tearing up the long drive from the main road. As the vehicles arrived beneath the elm trees in front of the house, they fanned out and screeched to a halt, doors were flung open and men dived out in all directions. Some crawled along the ground, others rushed for cover behind barn doors and herbaceous borders. My mother broke off from looking at her flowers and went over to call my father. ‘You had better come, Brian,’ she said.

What resembled the cast of The Professionals — shaggy hair, sideburns, leather jackets — now strode up the garden path to the clematis-framed front porch and produced their policemen’s IDs and a warrant to search the premises. They did not let on what they were looking for, but my father, in a woolly bobble hat and pink nose, welcomed them in. For the next several hours the coppers searched the house and many farm outbuildings high and low. I was at school at the time, but I later learned, to my great annoyance, that they rummaged through my chicken hutch, the barn where I kept my goats, the stables, the dovecote, my budgerigar cage and my fish tank full of Siamese fighting fish. They poked around among the middens, the haystacks, the piles of cider apples and down the old well. Still refusing to explain why they had searched the place, the coppers then thanked my very bemused parents and departed in the convoy of vehicles.

A few weeks later a report ran on the evening television news about a massive police operation involving 11 constabularies across the West Country. Scores of people had been arrested in raids that eventually, in Wales, discovered drug factories loaded with enough LSD to make 6.5 million tabs of acid. My parents looked at each other and thought about that police raid, launched so soon after the hippies had descended on the farm and Iddesleigh like Ken Kesey’s Merry Pranksters. This was the famous Operation Julie launched by the drug squad in 1978.

A few weeks later my mother was conducting one of her quite rare spring cleanouts of the rambling farmhouse when she found a suitcase under one of the guest-room beds. She called my father in and showed him the contents of the case. Pretty quickly, Dad worked out that it was a rather huge stash of grass. He immediately took it outside and put it on a bonfire of autumn leaves. As it burned, it produced a huge column of white smoke that spiralled into the North Devon sky. When he returned to the house Mum said his eyes were bloodshot and he was giggling. The sheep and cattle in the fields must have been stoned all the way to Hatherleigh that day.