“NO-ONE ever told me there was so much potassium in a banana,” recalls Tony Benn, to much amusement, as he records his final diary entry.

Though the man himself has been dead for five years and wasn’t prone to recording his innermost thoughts in front of a live audience, this engaging and immersive theatrical conceit, the brainchild of director Andy Barrett and director Giles Croft and based on Benn’s diaries, sees Philip Bretherton don a dressing gown, spark up a pipe and embark upon a remarkable performance as the formidable parliamentarian.

The challenges are obvious. Bretherton is over 20 years Benn’s junior, doesn’t immediately resemble the Labour Party stalwart and has to deliver a monologue, complete with those mellifluous intonations and Bennite mannerisms, for over an hour.

Yet he more than meets the task in just 75 minutes as he takes us on a comprehensive journey through Benn’s life, from his service in the air force during WWII and years as a young and promising MP, to his impassioned speeches against the invasion of Iraq and rather surprising status as a “national treasure.”

Throughout, he speaks directly to three people he loved and who are no longer with him — his mother Margaret, who imbued the young Benn with a keen sense of justice, his brother Mike, who died serving in the RAF in 1944 and his wife Caroline, stricken down with cancer in 2000.

Switching back and forth in time the narrative, thankfully, isn't linear. Connections are made in interesting places and recollections lead to a string of amusing anecdotes and touching memories.

This is a play that’s a reminder of one painful truth. Politicians of Benn’s calibre, integrity and unrepentant conviction are thin on the ground today. Yet while he may no longer be with us, Croft and Bretherton afford the possibility of spending some time in the company of his inspirational spirit.

Runs until April 20, box office: omnibus-clapham.org