The recent furore over London’s taxis has been especially relevant for actor, Ben Caplan.

The 43-year old father of two from Hertfordshire, who many will remember as PC Peter Noakes, screen husband to Miranda Hart’s character, Chummy, in Call the Midwife is currently starring in the stage version of The Knowledge, written by the late Jack Rosenthal, and directed by his wife, actress, Maureen Lipman.

“We’re flying the flag for black taxis” says Caplan, who plays Ted Margolis, from a dynasty of Jewish cabbies. “He’s surrounded by it. His family think he can’t do the Knowledge, so he resolves not only will he study for it at the same time as holding down a full-time job in a laundry, but he’s also going to pass in record time.”

To prepare for the role, he and fellow actors sat in on actual tests with would-be cabbies learning the Knowledge — memorising every street in London. “I was completely in awe watching them. It highlighted the nerves — it’s extremely nerve-wracking.”

He explains that the test remains much as it was in the 1970s.

“ It’s stressful to watch. I was really rooting for the three people I watched — two passed and one didn’t. Candidates are given two venues and asked to get from one to the other, road by road. The examiners can also throw in a curve ball like roadworks or a road closure. Get it wrong and it’s over.”

The actors each learned specific routes. Caplan’s was Manor House to Gibson Square (and back) and he says although he now knows it well enough to drive the journey himself, he’s still terrified reciting it on stage.

“As actors you are used to learning lines, but we get plenty of cabbies in the audience, so they know if we get it wrong.”

Being Jewish has helped him understand the cultural references, in particular, his character’s predicament. “I can certainly identify with Ted’s need to provide for his family and his drive to succeed.”

Caplan started acting in school productions at Aldenham School, joined the Young Vic Youth Theatre as a sixthformer and studied at The Royal Central School of Speech and Drama where classmates included Martin Freeman.

It’s not the first time he’s worked with Lipman. “I acted with her on a short piece for the UK Jewish Film Festival called That Woman about a guy getting set up on a date with Monica Lewinsky. Maureen played my mum. She’s lovely.

“We all want to do Jack Rosenthal proud and this is a faithful adaptation which is very true to what the original film was about.”

The play has given him a new perspective on the iconic black cab: “I’m glad we are shining a light on the sacrifice and dedication that goes in to becoming a black taxi driver.”

‘The Knowledge’ is at the Charing Cross Theatre until November 11