I have no recollection of my first time seeing Thin Lizzy in concert. It was at an outdoor gig in Blackrock Park, in south Dublin, on a sunny afternoon in 1970, but I didn’t pay a blind bit of notice to the three hairy guys on the stage, being just 11 years old and too busy eating my 99.

It was a family day out, and, as he did on many family days out, my dad brought along his 8mm camera, to film me and my younger sisters at play. Dad was an amateur film enthusiast. He’d film us on our Holy Communion, on visits to the zoo and on trips to the beach. He also used to make comedy shorts, using stop-motion animation to make us all run around really fast, like a kids’ version of a Benny Hill sketch. And he made little documentaries, such as one about the annual King of Dalkey festival.

When he was shooting a home movie Dad would make sure to get plenty of panning shots, to set the scene, so in Blackrock Park that day he took lots of footage of the band on stage and the audience of young hippies sitting on the grass and taking in the vibes.

Every year around Christmas Dad would set up the projector and screen, and the family would sit around and watch home movies. One evening, some time in the mid-1980s, he showed the film of our day out in Blackrock Park. There’s little Kevin, running around on the grass, oblivious to the band rocking out behind him.

“Wow, Dad, do you know that’s Thin Lizzy on stage?”

“Who?”

“Thin Lizzy – they’re the biggest Irish band in the world. That’s Phil Lynott singing. You’ve probably got the earliest known footage of Lizzy in concert.”

“Is that worth money?”

In 1995 the RTÉ presenter Shay Healy decided to made a documentary about Lynott, entitled ‘The Rocker’, to mark the 10th anniversary of his death. “The reason I did the documentary was that I didn’t want somebody who didn’t like him to do it. It could have been a stitch-up job – dead junkie, you know? I thought he deserved better than that. His wife, Caroline [Crowther], talks for the first time, and she said, ‘Philip was a rock star when he was brushing his teeth.’ ”

The documentary takes an in-depth look at Lynott’s life, career and death, and features interviews with former bandmates Eric Bell, Brian Downey, Scott Gorham and Gary Moore, and stars such as Bono, Bob Geldof and Van Morrison. And it features archive footage of Lynott, including my dad’s accidental concert movie.

“It was just three of them: Philip, Eric Bell on the guitar and Brian Downey on the drums,” says Healy, confirming that this was indeed an early incarnation of Thin Lizzy on the stage. Eric Wrixon had already left, “because, he said, with all the drinking and drug-taking, he would have died”.

Healy says that Lynott is the premier icon in Irish rock music. “If he’d lived he would have gone on to great things as a solo artist. He had great style and panache. He always said, ‘When I’m in England I’m from Ireland, when I’m in Ireland I’m from Dublin, when I’m in Dublin I’m from Crumlin, and when I’m in Crumlin I’m from Clogher Road.’ ”