As a psychiatrist turned actor, Dr Julian Bird was a shoo-in to play Sigmund Freud at the end of his life.

Freud's Last Session at The King's Head is set in the father of psychoanalysis' Hampstead study at the outbreak of World War II and imagines his lively encounter with author CS Lewis.

The 80-year-old, who trained as an actor in his 60s after a distinguished career at The Maudsley Hospital, said: "The play is witty and well researched and doubly fascinating to me because I am interested in both characters and I'm a psychiatrist in my other life.

"It's set just as war is declared - the BBC news sets the tone - and Freud's account of his escape is part of the play. It was a huge challenge for him to get out with his family and bring his belongings with him, he had to bribe a lot of people."

Despite suffering from cancer, the 82-year-old was forced to flee Vienna when Hitler annexed Austria. Arriving in London in June, 1938, the Freuds moved to 20 Maresfield Gardens, as he wrote: "our last address on the planet". But as his illness progressed Freud died there on September 23, 1939.

As well as visiting what is now The Freud Museum to "soak up the atmosphere," Bird's preparation for playing the dying Freud was to "look for the pain."

"That's my personal way of trying to get to the root of what makes a person tick. Freud's upbringing was a mixture of cultural clashes, he didn't have a loving relationship with his father, he despised him and that fed into who he became as an adult. He was passionately wedded to trying to understand the human condition and had a strong sense of his own importance and how vital it was that the world understood his ideas. He wasn't an easy man to get along with but he had a passion for inquiry."

Although Salvador Dali, Virginia Woolf, and HG Wells visited the house, Freud's meeting with Lewis "probably never took place." But playwright Mark St Germain uses the fictional encounter to couch a lively intellectual debate about sex, love, and the existence of God in a battle of wits between rationalist Freud and the Christian Oxford Don.

"While Freud himself was passionately atheist and thought all organised religion was 'infantile nonsense,' having lost his faith, CS Lewis had a conversion experience and became an evangelical Christian," says Bird. "There is truth to be told in the play. If they had met, Freud would be genuinely fascinated by that conversion and want to understand it."

It was a cancer diagnosis that led Bird to take up acting.

"I had a series of very unpleasant operations, at one stage I thought I was soon to die and wondered what I was going to do with the time left. In the event I recovered, but during that period of re-evaluation big decisions got made."

Bird's mother Freda Jackson was a stage and screen actress who had her breakthrough in 1945 at The Embassy Theatre, now part of Belsize Park's Royal Central School of Speech and Drama. His father Henry Bird was a set designer and Freda was part of Sir Laurence Olivier's National Theatre as well as acting in his film of Henry V and David Lean's Great Expectations.

"Having been brought up in a theatre family it brought back lots of childhood emotional stuff that was the basis of the decision to do something completely different," says Bird. "My mum's breakthrough was a curious link with the Royal Central school where I did an acting course for mature students. When I walked into the auditorium on my first day I had an image of my mother playing on that stage in No Room At The Inn. It was a scandalous play about the abuse of orphan children who had been evacuated during the war and it transferred to the West End. People didn't like the idea that kind of thing was going on and my mother had death threats."

At Central, Bird "had a ball". "I assumed it would be awkward but I wasn't treated as some weird old wrinkly out of place. The theatre world is not like that, mostly people are accepted for who they are and what they can do. I wasn't at all sure whether I was would be any good at it but I got hooked and it's become my life. Theatre for me is more enjoyable than film or TV, there is nothing like the special relationship with a live audience."

Now retired from clinical practice, he can nevertheless bring his experience to playing Freud.

"Although I am not a devotee of his theoretical framework one thing we share is a fascination with the hidden reasons that drive people's behaviour."

Freud's Last Session runs at The King's Head, Islington from January 18 to February 12.