At first sight across the room in a smart west London media club, where I am about to meet Adam Kay, he looks comfortably settled at a corner table. But, as I approach, I notice he is wearing an orthopaedic boot and has a pair of crutches stowed on the seat behind him.

My immediate thought is that, as a comedian, Adam Kay will know what a “pratfall” is. And, having been educated at both Dulwich College and Imperial College London, he will doubtless be familiar with the term, “nemesis”.

If that sounds unkind of me, it isn’t intended to be. It’s just that I am reacting to Kay’s present condition in the spirit of his own hilarious, humane and sometimes harrowing book, This is Going to Hurt, based upon diaries he kept a decade or so ago as a junior doctor, in which his view of practitioners of the skills from which he has so recently benefited reads: “Orthopaedics is basically reserved for the med school’s rugby team — it’s barely more than sawing and nailing — and I suspect they don’t ‘sign up’ for it so much as dip their hand in ink and provide a palm print.”

Now, he says, after treatment for a broken ankle having slipped on a wet pavement getting out of a taxi — pratfall, nemesis — “I have nothing but love for orthopaedic surgeons.”

Actually, the book is infused with love throughout — certainly love of life, and indeed of the profession that Kay eventually quit, for utterly understandable reasons that he movingly describes at the end of the book. By then, he has made you laugh at situations both inherently and outrageously humorous, squirm at graphic examples of work at the medical coalface, sadden at the tragic and sympathise at the stressful. With regard to the latter, the words “long hours for low pay” don’t begin to convey the reality of hospital life as lived by junior doctors.

After leaving medicine to be a stand-up comedian, Kay is now enjoying success as a writer and script-editor for television, having worked with Sasha Baron Cohen in America and, inter alia, on Mrs Brown’s Boys in the UK. So does he miss his old job? “I certainly don’t miss what a ‘bad day’ means. Now, my ‘bad days’ are frivolous — when a sitcom gets bad ratings or reviews. I do miss having colleagues; there’s something quite solitary and lonely about writing.

“I also miss the non-specific feeling of having ‘done good’, when you’re driving home knackered and blood-splattered, four hours late and the dinner’s in the cat, but with the feeling that you’ve somehow been a useful member of society — which I think is why people do medicine in the first place. Nobody becomes a doctor for the money. The remuneration is out of step with the responsibility at all stages of medicine.”

In this connection, Kay argues that, if Jeremy Hunt, the Health Secretary, spent a shift shadowing a junior hospital doctor, taking in the gory with the glory, he would understand what it means to be one: “If the choice is to go home on time, and someone dies because they’re bleeding out in front of you, or to stay because there aren’t extra people to help,” he says, “you stay and do it. The stakes are too high.”

He had “absolutely no intention” of turning his diary notes into a book when he was writing them. “As a junior doctor,” he explains, “you’re required to keep a log of everything you do. I guess the frustrated writer in me also wrote down anything funny or weird or interesting that happened to me. Writing wasn’t my passion but my plan B and it had to involve comedy because I did do a bit of that — in the tradition of medical-school revues. Then, by sheer coincidence, my comedian and novelist friend Mark Watson came to my show and brought along his publishing editor from Picador, just as a plus-one, and she said to me afterwards: ‘you know that’s a book’. It hadn’t occurred to me.”

The publication of This is Going to Hurt has helped reconcile Kay’s family to his aborting of his medical career. “I didn’t tell my parents the details of why I quit. I just said, ‘I’ve left medicine’. They weren’t impressed. I couldn’t talk about it. It’s only now, with this book, they actually know the ins and outs of why I left. At the time, it was as if I’d gone home and said: ‘I’ve joined the circus.’”

Home was in Dulwich in south London, “a Jewish-ish home. I went to cheder. Had a barmitzvah. I consider myself extremely culturally Jewish. It means a lot to me to be part of a — lower-case ‘c’ — community. I go to shul once a year max.”

Though he has left it behind, Adam Kay will always carry the indelible stamp of his time in medicine, as is clear from the outstanding This is Going to Hurt — which is not, it has to be said, for the faint-hearted. For example, having specialised in obstetrics and gynaecology, Kay offers snippets of his intimate knowledge of basic female physiology, knowledge which he contrasts with the ignorance of other men, including husbands and partners of his patients.

In one diary entry, he describes disappointing a fellow party guest, ‘Danny’, by not recognising him as the TV presenter that he is but merely as the husband of a woman whose baby Kay had delivered by caesarean. ‘Danny’ jokes that he’s glad it was a caesarean because he’d be uneasy talking to a man who’d seen his wife’s vagina.

Kay’s account continues: “I want to say that actually I’d have seen it when catheterising her for the procedure, plus, if he really wants something to get his brain imploding, I’d have seen its reverse side during the operation. I don’t say this, just in case he wasn’t joking …”

‘This is Going to Hurt’ is published by Picador at £16.99