In his fourth book, Vet in Harness, James Herriot describes an incident in which he travels with Granville Bennett to a veterinary society meeting in Appleby. They drive over the moors in a violent snowstorm but, amazingly, arrive safely. After the meeting, he and Granville – fortified with good food and fine ale – return at incredible speed over the wild, snowbound road, only to discover the following morning that the road on which they had just travelled was reported to have been blocked for days!

It was, in fact, that redoubtable pair, Basil and Denton, who made the white-knuckle ride to Appleby and back, and it was after hearing about it from Basil one night that Alf took out his notebook and marked the incident as one to form the basis of a good story in a future book. This is another example of his using author’s licence; the story did not happen as he told it but, as with so many others, it was based upon a real incident.

‘It Shouldn’t Happen to a Vet’ was another box office success. As excellent family viewing, it was a change from the increasingly violent films that were being released at the time. Although Alf, in fact, enjoyed many films in which sex and violence were the prominent feature, he was still pleased that this wholesome film was one to which the whole family could be taken safely.

Donald seemed to approve of the way that he was portrayed this time. We were all very relieved, especially as one scene in the film compares Siegfried with Adolf Hitler, describing him as a ‘mad sod!’ Alf seemed to be more upset about this than Donald who, after completion of the film’s shooting, threw a big party in Southwoods Hall for all the cast and several of his friends. Donald was in great form at the party, laughing and chatting with everyone. Who could have forecast the throwing of such a party when, two years earlier, he was threatening his partner with litigation?

John Rush, the agent in charge of film and television rights at David Higham, in common with many others, always thought that the Herriot books were not ideal material from which to make a feature film and that, being episodic, they were far better suited to a television series.

Before the making of the first film, he had tried unsuccessfully to interest television companies, but it was not until after the release of the second film that the idea for a television series was put into place. David Susskind, the American who owned the right to produce any spin-off series following the films, eventually sold his interest to the BBC and, in 1977, a new group of actors assembled in the Yorkshire Dales. James Herriot’s stories were to be filmed yet again, but this time, they were to be beamed into the homes of millions.

The books and films had made the name of James Herriot famous but the television series, ‘All Creatures Great and Small’, turbocharged his popularity. It was after this series that the number of tourists visiting Thirsk rocketed to unbelievable proportions. His famous characters had now infiltrated people’s sitting-rooms and they liked what they saw.

Once again, Alf took a back seat when it came to being involved in the production. He approved the scripts – many of which followed the storylines of the books closely – but nothing more. He was quite content just to pay regular visits into the Dales to watch the actors at work. Jack Watkinson, the vet in Leyburn, acted as veterinary advisor in the Dales, while, with much of the studio work being shot in the Midlands, my father’s old friend, Eddie Straiton, provided the professional expertise.

The part of James Herriot was played by Christopher Timothy. Up until this time, he was not well known to the public but it took only one or two episodes on the television to propel him to stardom.

Chris Timothy developed a lasting respect for Alf Wight, a man he felt proud to have played. He was diffident about meeting him for the first time but, after his first introduction on the film set in the Dales, was soon put at his ease.

While fishing in Swaledale one day, and sensing a tap on his shoulder, he turned round to face a man he did not know.

‘Are you Chris Timothy?’ asked the stranger.

‘I am,’ replied Chris.

The man continued in a quiet Scottish burr, ‘Well … I am your alter ego.’

Chris liked him from that first meeting and he never lost his affection for my father, whom he described many years later, as a ‘private, totally approachable, totally delightful, up-front guy’.

For their part, of all the stars Alf and Joan met during those intoxicating years, Chris has been the one who has kept in touch with the family more closely than any other. He continues to visit my mother whenever he is nearby, and often sends letters from abroad whenever his acting engagements take him further afield. Chris, who has appeared on many factual programmes about James Herriot, has been incredibly supportive of anything that has involved the man to whom he feels he owes so much. His role as the famous vet, one which gave an enormous boost to his career, is something he has never forgotten.

I shall always remember his unflinching cooperation when asked to speak at my father’s Memorial Service in 1995, together with the wonderful performance he gave when reading the passage from Vet in Harnessabout that great composite character, ‘Biggins’. Chris was pleased we had chosen that particular episode since he had become friends with the actor who played Biggins in the series, who had himself sadly died prior to the Memorial Service.

If Chris Timothy was a comparative unknown before assuming the mantle of James Herriot, the actor who played Siegfried – Robert Hardy – most certainly was not. He was already an established and much-respected performer and, as well as having experience as a Shakespearean actor to his credit, his versatility was such that he had stepped expertly into the roles of such diverse personalities as Winston Churchill and Benito Mussolini.

I remember my first meeting with Robert Hardy. One afternoon in the surgery in 1977, I was surprised to see a figure in a white coat, counting tablets into a bottle beneath the disconcerting stare of Donald Sinclair. Seconds later, Donald seized the bottle.

‘No, no, Tim! I’ve already told you! These tablets are for dogs only! You nevergive these to cats!’ I wondered who this unknown, brow-beaten employee of the practice could be? I looked more closely at him. ‘Good heavens, it’s Robert Hardy!’ I said aloud.

His smiling face turned towards me and Donald introduced us. ‘I am very pleased to meet you,’ he said. ‘Call me Tim. That is how I am known to my friends.’ I took an instant liking to him.

With filming having only recently begun, he was spending a few days at Southwoods Hall with Donald to give him the opportunity of studying his character. It proved, not surprisingly, to be a most illuminating experience and his time was obviously well spent because his portrayal of Siegfried, a character whom he came to love dearly, was brilliant. Although he bore no physical resemblance to the real man, he captured his impulsive character perfectly and his performance passed the severest possible test – the approval of the Yorkshire farmers who knew the real Siegfried so well. ‘By! That feller teks auld Sinclair off well!’ was a cry that I heard countless times.

Donald and Robert Hardy became the best of friends over the years but, true to form, Donald did not approve of his television portrayal. Almost twenty years later, in 1996, I had the pleasure of seeing Tim Hardy on the top of the White Horse Bank, near Thirsk. He had come to open officially the White Horse Preservation Society, an organisation dedicated to the upkeep of the famous White Horse that had been cut into the hillside above the village of Kilburn over a hundred years ago. He gave a short but revealing speech in which he reminisced about his role as Siegfried.