The Magical Mystery Tour was sold to the BBC for, I think, around £10,000 and got shown on Boxing Day 1967, shoved between a Petula Clark show and the Norman Wisdom film The Square Peg. It got well and truly slaughtered by the critics. The Daily Express called it “blatant rubbish” and Paul went on the David Frost show the next day to defend the film, though he admitted it had no point or aim.

I think one reason for the criticism was that, after five years of Beatlemania, worldwide adulation, and the band being the best-known people on the planet, blah blah, a lot of the media was looking for a chance to take the Beatles down a peg or two, especially when they appeared to have been condoning drugs.

Before the TV audience got to see it, I’d been to a private viewing for friends and family at London’s Royal Lancaster Hotel on 21 December. We had been told to come in fancy dress, which I moaned about. My wife and I went as a girl guide and boy scout, wearing stuff borrowed from some kids in our street, which didn’t fit.

Everyone else had hired really expensive costumes. Paul and Jane Asher, his girlfriend at the time, came as a Pearly King and Queen (left) and looked sweet. John was dressed as a Teddy Boy and looked menacing. He wore a drape jacket, drainpipe trousers and brothel creepers, and had his hair greased back. John appeared rather distant, switched off, not much interested, which is how he had been during most of the filming. Later he tried to disown it, saying it was all Paul’s doing; he was just dragged along.

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For a year, they had put off doing a third Beatles film, after A Hard Day’s Night (1964) and Help! (1965), then on a flight back from the USA with Jane, Paul had thought of this idea of doing an hour-long TV film in which they would all get on a bus, shoot stuff, see what happens. It would be mysterious, as no one would know where they were going. And magical, so that they could do what they wanted.

The “Mystery Tour” notion harked back to their childhood, something very common in the 1950s, which you hardly see today, and was popular with working-class families in the North who didn’t have a car. In Carlisle, when I was growing up, you always ended up in the Lakes, so it was never a huge mystery. A crate of beer would be taken by the dads and everyone would sing on the way home.

It was another six months before Paul firmed up the idea, by which time Brian Epstein was dead. They now had no manager to calm them down or give back-up from an office. So they really did set off with little planning and no proper script, just asking some character actors – whom they admired, but didn’t audition – to come along.

Paul, in his naivety, thought they could just turn up at Shepperton Studios to shoot the big scenes, not realising that such places have to be booked up months if not years in advance. Instead, they had to mock it up in an old airfield at West Malling in Kent.

When it came to the editing, Paul set aside two weeks – but in the event it took 11 weeks, hacking down ten hours of film into 50 minutes.

I used to go to see him in an editing studio in Old Compton Street in Soho, up some stairs above a dodgy club. Outside there was often an old drunken tramp with carnations behind his ears who did a funny dance on the pavement. Paul was amused and would invite him up the stairs – which led to more delays as they couldn’t get rid of him. His party piece was Bless ‘Em All, with obscene words substituted.

At the time, watching Paul directing the film – which in essence he did – and then editing it, I thought how amazing it was that this young lad, with no training in film technique, was working it out all for himself, doing it his way.

They had, of course, written all those songs without being able to read or write a note of music, and made all those records with no studio experience. This was their philosophy. You could do these things if you really wanted. No need to follow the rules or be bossed around. A very modern concept. Though it did help to be multimillionaires.

They should, of course, have worked harder on the script beforehand and planned all the scenes in advance, but the idea was to make it spontaneous, and provide family amusement over the festive season.

As a Beatles fan, then and now, I greatly enjoyed it. It was a modest, short film, done on a budget. I couldn’t see why the clever-clogs critics were so beastly. And of course it does have some great Beatles tunes, such as I Am the Walrus, which has survived the test of time and Russell Brand mucking it up at the Olympics.

Then there is The Fool on the Hill and Your Mother Should Know, both written by Paul. The way the songs were shot was ahead of their time, self-contained little rock videos. Over the decades the film has acquired a bit of a cult following. It’s shown on Monday for the first time in 33 years, after an Arena assessment of it – it has improved with age, as we all do, tra la…