In 2005 in London, I came across the most unusual script I’d ever seen. The 10 or so pages looked like sheet music. Each phrase or word was separated with three dots and sometimes just two dots and a dash. But when I began to read, I didn’t hear just one narrative: I saw a transcript of how the mind works. Not a linear stream of thought, but layers of interjections, interruptions, insurrections. In-between the pure poetry and the scattering of Christian pieties, acerbic parochial asides – I heard the nuns, streets of sarcasm, scorn, gossip, humour. I heard home.

My director Natalie Abrahami banned any mention of Beckett's most famous muse Billie Whitelaw from the rehearsal room. She understood that I would need to find my own way. I had to arrest each phrase and lock it to something deeply personal. Since it was meant to be spoken at the speed of thought – in order to, as Beckett said, "play on the nerves of the audience and not its intellect" – I had to exercise extreme technical precision and emotional clarity.

It must be an awful business being a director of Beckett. He takes care of most of it from beyond the grave. Directors must of course select and lead the actors, towards and through his score, but then at a certain point, in order to serve the work, they must let go.

As for actors, Beckett can’t seem to squeeze enough out of us; there is not a cell in our bodies that isn’t constantly required.

Few know what it is to have your entire nervous system splayed open like that. Few know what it is to be suspended in that darkness, and to go on to perform one of the most difficult pieces ever devised. But there is one who knew more than most.

‘My own way’

I met Billie Whitelaw in 2006 a few months after my first performance of

Not I

in London.

Edward Beckett

attended one those performances and over a Guinness with me afterwards suggested it might be finally worthwhile to meet her “now that I’d found my own way”.

As luck would have it, a few weeks after that the BBC put us in touch for an in-conversation piece about the role. Until that point neither of us had ever met anyone who had played Not I. We greeted each other like two war veterans and swapped our trench stories. I told her how I strap my head into the banisters at home and babble away for hours, training my mouth and diaphragm to speak at the speed of thought without moving a millimetre.

Billie’s head, by contrast, had been strapped to a dentist’s chair. Once, during rehearsals, she collapsed, and Sam rushed over to her saying: “Billie, Billie what have I done to you?” Coming to, she replied: “I really don’t know how to answer that Sam.” “Never mind,” he said “back you go.”

“I would have walked on glass for that man,” she said.

She never felt she quite recovered from that role and none of his other plays – including the ones he wrote for her, Rockaby and Footfalls – had taken quite the same toll. "I lost a piece of me in there and it never got any easier," she told me.

A year after our first meeting I received a call from Billie: “I want to give you his notes, I have to give you his notes.” Standing in Billie’s kitchen later that afternoon, I thought she might dust off an old rehearsal manuscript. Instead, she told me to sit down at the table and “Begin”. As I started speaking, she sat directly opposite and began waving her hand, conducting me. “Ta..ta..ta..tah...Ta..ta..ta..tah.” This was exactly what Beckett had done to her, across her kitchen table.

Billie saw how I strained to hold back the tide of the Irish voices, the sounds and the effect of what the very notion of home produced in me. I understood that Beckett didn’t want the actor’s craft, but he did want emotion, only he wanted all of it – the real stuff, the guts – not some polished fool’s gold.

In 2009 I was invited to perform Not I as a stand-alone piece in the Southbank Centre, so Billie and I stepped up our sessions. On opening week, Billie was admitted to hospital and has never returned home. On the morning of opening night, she told me to come by, and she again conducted me from her hospital bed.

Since then I’ve produced the work myself and I’ve realised that this has been my saving grace. Travelling though the darkness of the work, it forces me to keep one eye open and maintain a healthy perspective. That, and Billie’s parting northern wisdom: “Just get on with it.”

Beckett's friend and biographer Jim Knowlson was in the audience that opening night. He wrote to Beckett's long-time collaborator and assistant director Walter Asmus, saying we must meet me. Asmus, hearing I was in my mid-20s, was unconvinced: "Another actress trying Beckett . . . "

When Edward Beckett heard I was putting on Not I in the Royal Court Theatre he came to my flat and, using all his knowledge as a professional flutist, he helped me rehearse. She's were elongated; ellipses tightened; tempo was balanced and diction sharpened, all with a musician's precision. When I think of the time that people have given freely to me over the years, I realise this work is more like a vocation than anything I've ever known.

Asmus was in the audience at the Royal Court. Afterwards he offered to direct me in Footfalls and Rockbaby, and put them as a trilogy with Not I.

Physically possible

I wasn’t sure that performing these three together was even physically possible. We headed to an isolated cottage in Co Monaghan to work things out.

He often said when rehearsing Not I: "It's coming too easy to you – it needs to cost you more, we need to see you bleed up there." He persisted when I offered anything less than truth. When we began with Rockaby, Walter wouldn't let me get past the first six lines for weeks. I felt so hemmed in, so panel beaten.

I only later realised what he was doing was getting me totally technically aligned – with my tone pitch perfect, my arms outstretched to allow the breath into the voice – until suddenly one day he let me go, and I caught an invisible current. I needed that momentum to take me right to the end of that piece to face the loneliest truth of all; that I am my “own other . . . living soul”.

When I looked up, Walter was weeping.

And that's what I do when the bell goes for the first time in Footfalls. With each of those footsteps I open up wounds that will hum his taut tempo. I summon instruments that will play Beckett's score in the raw and in the real. Around his solid structure I must wrap material of my own. And suspended in that dense darkness I must also weave in the slow rumble of a train under the Royal Court stage, a seagull's cry from above a theatre in Galway, roaring sirens in the West End, even the frightened cough from the man in the front row.

It’s at this precise moment that I must show the greatest courage and commitment. I can’t select the off-cuts of feelings. It must be the meat itself.

One of the gifts of the sensory deprivation in Not I is that I don't even feel like a human being half the time up there, and that's so liberating. Who's going to want all that from me? We tend to view ourselves and our world in bite-sized chunks – what we think we can cope with. We create pithy palatable realities shaped by our small prejudices and fears.

Beckett blows all that up and offers instead the most enormous landscape where we must bring everything we are and could possibly be to it. No other writer I have ever come across has ever asked or offered so much.