Back in 1992, Catherine Johnson wrote a show for her local theatre that skilfully worked Ska revival tunes into a tale of inner city love.

Too Much Too Young was “like a gig going off every night” in the Bristol Old Vic studio says the 56-year-old playwright.

A few years later, it became her “calling card” when producer Judy Craymer was seeking a writer to weave the ABBA songbook into a musical.

Although no great fan of the Swedish pop sensation, Johnson gamely set about the task, creating the hit musical Mamma Mia!

“The punk Ska era was where I was musically most inclined but I always loved music and worked in a record shop for a few years where you needed to listen to everything.

“That’s where my ABBA experience came from.

“I got in all the latest punk releases for the few who were interested and once freaked my manager out by ordering 75 copies of The Specials’ Gangsters. We were the only shop for miles and I knew they would sell – I pride myself even then on my ability to spot a hit!”

When she sat down with the ABBA songs, Johnson quickly formulated a plot about a single mum and a daughter looking for her dad.

“I was extremely lucky in being gifted a catalogue that worked as storytelling songs.

“I had a vague plot outline and as I worked with the lyrics, the characters started to come to life. I thought, ‘My God it’s all there! This is going to work.’”

It was more successful than inferior ‘jukebox musicals’ that shoehorn in a back catalogue, because “if you have songs that tell a story you are well on the way to making an enjoyable engrossing night out where the story isn’t broken up when people start singing to one another but keeps going, and every song earns its own keep.”

Surprise

Even then, Johnson thought the show might run a few months until she saw her ABBA/musical theatre-hating brother-in-law dancing in the aisles on the first preview.

“I never knew it would be a big hit or that I was writing the thing that was going to keep me out of the red for years, but on preview night I realised it was something special.”

Having previously worked in small subsidised theatres, Johnson was unprepared for that level of commercial success. And when Craymer insisted she script the subsequent film, starring Colin Firth, Meryl Streep and Pierce Brosnan, it became atone point the highest grossing British film.

“Being in meetings where no-one speaks to you because you are the writer was like a scene from all those books. I kept thinking I’d be replaced but to my surprise I stayed with it. I’m so glad the script was ready by the time Meryl was cast because if I knew I was writing lines for Hollywood royalty I might have frozen.”

Islington’s King’s Head theatre is reviving Shang-a-Lang, a pre-Mamma Mia! foray into 70s music, which co-opts Bay City Rollers tunes into a story of mid-life crisis.

It follows a group of 40-year-old women reclaiming their youth at a 70s revival weekend at Butlin’s.

“I was too young for the Bay City Rollers, but I wanted to choose a band for a 70s tribute weekend that women would have this kind of obsessive love for when they were younger. Plus they were theatrically and visually interesting – there’s nothing like that tartan to plunge people back into that era.”

Far from being a shamelessly sentimental yearning for the past, Shang-a-Lang is “an anti-nostalgia play”, says Johnson.

“I wrote it when I had just turned 40 as an antidote to this constant harking back to another time and the idea you are leaving your best years behind.

“As someone who hated being at school and in my 40s was about to come into the best days of my life, I really wanted to do something that explored the possibilities at 40. It’s a great turning point, if you are unmarried, and haven’t a family you might start regarding yourself as a bit of a failure, but it’s also a mid-way point where you are entering the downward slide into oblivion but not quite beaten into submission by life.

“You still have the possibility of changing yourself if you are bold enough.”

If Pauline doesn’t recognise that her best friend Jackie who she envies has an unhappy marriage, Lauren is 40 going on 14 – with a “complete disregard for convention and niceties”.

“She’s one of my favourite characters, my secret self if only I had the gumption.”

Johnson, however, did show gumption when she moved to a housing association flat in 1988 as an unemployed divorcee with one toddler, and a baby on the way.

“I always wanted to be a writer but life got in the way. I was hitting 30 and thought, ‘This is it’.

“Until that point I was quite lazy about doing anything fulfilling and I made a pledge to myself to spend a year trying to write. If that didn’t work I would train for a grown-up job like probation officer or social worker.”

“Hollywood-style” she immediately spotted an advert in her local paper for a playwrighting competition. She would rise at 4am to write before her son awoke, and “managed to get this play out of me”.

Winner

Rag Doll, a drama about incest and child abuse, won and was staged at the Bristol Old Vic, directed by playwright Terry Johnson: “A fantastic mentor who knew how to talk to me in a way that wouldn’t send me shrieking back to the flat howling, ‘This world is too scary’.”

Johnson, who still lives in Bristol and has two grown-up children, went on to write for TV and stage before that fateful call from Craymer.

But perhaps because of early hardship she had a tough time accepting success.

“It was a real sideswipe to how I had expected my career to be, and much more difficult than I thought it would be to accept. Some of the message I wanted to get in about single parents rolling up their sleeves and not just being scroungers, seemed to get a bit lost, but Mamma Mia! has given me the freedom to do smaller projects, and I have lots of ideas.”

Shang-a-Lang runs at the King’s Head until February 15.