By that time he had already seen David Lean's big screen version of Noel Coward's play, Blithe Spirit, in which Margaret Rutherford's eccentric medium Madame Arcati inadvertently conjures up the ghost of Rex Harrison's novelist Charles Condomine's dead first wife, Elvira.
"My first live experience was going to watch psychics with my aunties at the spiritualist church," McKnight says. "I think that is what got me into theatre. There were times when you just thought the psychic was a fraud. But there were others who were so on the money that you wonder how it could possibly be faked. There were times it was heartbreaking. Every week there would be the same two rows of people, who had clearly had a bad loss. It was two rows of desperate sadness looking for peace."
McKnight's formative experiences at the spiritualist church filtered into his own work with Random Accomplice, the company he co-founded and still runs with Julie Brown. Assorted psychics and fortune tellers have made appearances in Little Johnny's Big Gay Wedding, Something Wicked and Marymassacre.
It is only fitting then, that for his first foray into working on classic drama rather than new work that McKnight should direct his own production of Blithe Spirit. For a director weaned on pantomime and all things camp, however, McKnight's Blithe Spirit promises to take a very different approach than the cut-glass quick-fire reverence with which Coward's work is usually treated.
"I find it slightly weird when you go to see Coward," McKnight says, "and everyone talks in these posh English accents. You find yourself concentrating on all these posh people being witty rather than concentrating on the story."
With this in mind, McKnight has relocated the play from its original Kent setting to the theatre's Perth doorstep.
"The first week of rehearsal was all about trying to unpick an intonation and a rhythm that you know so well," McKnight explains. "It was written for a middle class voice, so you need to find another rhythm and freshen things up. That has helped the cast from the start, I think, because it has freed them up to not play it like the movie.
"When Elvira says to Charles that he was beastly to her, when you look at it, there is something quite fiery going on there. That goes with the look of it too. Let's not have the ghosts floating about flatly in grey fibre. Let's put them in scarlet, because they are the most alive people in the room."
One challenge for McKnight has been reconciling himself with the play's ending, which was changed for the film.
"I know the movie so well," he says, "so I forget how misogynistic the end of the play is. In the film Charles gets his just desserts, and it is a total Hollywood ending, with them all ending up dead together.
"In the play Charles wins the day, which is all about Noel Coward being so against the institution of marriage. It has been funny reading up on it, because there was one thing I read that suggested the ghost was an expression of homosexuality coming out of the closet, but I don't see that at all. Basically, Coward just hated marriage, and it is no coincidence the happiest people in the play are all single."
McKnight's production of Blithe Spirit comes at an interesting time for Perth Theatre, and for Horsecross, the organisation in charge of it.
As the theatre prepares to go dark for two years while it undergoes a multi-million pound refurbishment, the announcement of the departure of Rachel O'Riordan, Horsecross' director of theatre, to become artistic director of the Sherman Cymru company in Cardiff has come as a surprise.
Since her appointment three years ago, O'Riordan's bold programming and directorial verve has made Perth Theatre a serious player in Scotland's theatre scene, with her production of Conor McPherson's play, The Seafarer, picking up several awards. It was O'Riordan too, who drafted McKnight into the building.
"She is a dynamic force," McKnight says of O'Riordan. "The work she has put on during her time here has been accessible, but has never played to audience expectations. Her new job in Cardiff is brilliant for Rachel, but it is a great loss to Perth, and to the whole of Scottish theatre. She is going to be a tough act to follow, and I just hope the board manage to find someone just as dynamic."
It was O'Riordan, too, who persuaded McKnight that tackling a classic play rather than the new work he is best known for was a good idea.
"I am used to having writers in the room with me, who I can ask questions about the script, but I can't do that with this," he says.
"You have to bear in mind that Coward wrote Blithe Spirit in five days, and when you look at it closely and break it down, you realise a lot of it does not make sense, but that it has a kind of panto logic to it. It goes so fast when you play it that you don't notice the plot holes, and there are lots."
McKnight's radical approach to Blithe Spirit may cause Coward purists to raise an arch eyebrow or two, but this does no mean McKnight is not taking the play seriously. Far from it, in fact.
"The play is still funny," he says, "but I hope it will feel not quite as flimsy as it sometimes does. I hope there will be flesh and blood and bones there as well. I don't want it to be knockabout. I want there to be some kind of truth of the moment there as well. Madame Arcati is still funny, but there is something deeper going on than her just being a mad old boot."
Blithe Spirit, Perth Theatre, October 30-November 16 www.horsecross.co.uk