When it came to casting the TV adaptation of his children’s book, Dexter Procter, The 10-Year-Old Doctor, Adam Kay took a very direct approach.

Many of the familiar adult names who star in the forthcoming show have told how they received ‘sweet’ emails directly from the former medic asking them to take part.

Peter Serafinowicz, who plays the title character’s nemesis, Dr Drake, said: ‘‘Adam wrote me such a sweet note asking me to consider this role, and he even included a drawing of the character. 

‘We’d never met, so we spoke on the phone for about 40 minutes. He was so funny, and we had such a laugh - I thought, "I really want to work with this guy.’

Upstart Crow star Gemma Whelan, who plays Dexter’s mum, said: ‘I received a very nice photograph of a handwritten note from Adam via my agent… and I said yes immediately. I was familiar with much of Adam's other work. He's a very good person to be familiar with as everything he produces is excellent.

And Jameela Jamil, who plays teacher Miss Melon, said: ‘Adam wrote me the loveliest and most charming email asking me to take part, and as a huge fan of his, it was an immediate yes.’

Probably Kay’s easiest sell was asking Mike Wozniak to play Dexter’s dad – as they have been friends since they were  both at medical school aged 18. They were even in a medics’ sketch group together called Handjobs for Crack, which Kay has subsequently described  as ‘homeopathically weak’.

The personal touch certainly paid off as Kay says: ‘We sent the script out to my dream list of potential actors and, one by one, they all said yes – it was a totally pinch-me week.

‘They say you should never meet your heroes, but they’re totally wrong – I met about a dozen of my heroes on this show and they were all wonderful people as well as wonderful comic actors.

Casting the young actor to play Dexter himself was a more involved process, but Kay says: ‘The second I watched Cian [Eagle-Service’s] audition tape I texted the rest of the team with "WE’VE FOUND DEXTER!" and they all absolutely agreed. 

‘He is genuinely one of the best actors I’ve ever worked with, of any age. He nails the comedy in every single scene as well as playing Dexter’s charm and vulnerability. If he doesn’t end up winning a Bafta at some point, I’ll eat my Bafta’.

Kay also reflected on the ‘long tradition of medics becoming comics, from Graham Chapman in Monty Python to Graeme Garden in the Goodies. Plus a bunch of people not called Graham, like Harry Hill, Paul Sinha and Simon Brodkin, as well as nurses like Jo Brand.

‘Maybe it’s a case of using gallows humour as a coping mechanism, or maybe it’s just people looking for an alternative to 95-hour weeks and getting covered with bodily fluids,’ he added. ‘But the NHS’s loss is Dexter Procter’s gain – both me and Mike Wozniak who plays Dexter’s dad are former doctors and in fact, we’ve been pals since we were both at medical school.’

Reflecting on the same topic, Wozniak says: ‘There are a lot of people in medicine who have other passions. Plenty end up in medicine because they drift into it - maybe someone notices they’re good at passing exams, which is its own skill and not necessarily the same as being clever. So they tick the right boxes, and suddenly they’re on that path.

‘But before med school, many had deep passions - music, sport, art, acting, writing. Where I trained in Tooting, we were drowning in incredible musicians. There were sporty types, arty types, people who might have wanted to be actors or playwrights. Comics are just one small group within that mix.

'I think it’s slightly easier for comics to make a go of it because you can sneak off when you’re not on call and do a gig. If you’re trying to get a band going or play rugby for Wales, that’s much harder to squeeze in. So comics maybe slip through the net a little more easily.’

Meanwhile, Jamil also has first-hand experience of working in schools as she was a teacher before she was famous.

But she admits: ‘I was a terrible teacher. Much like Miss Melon. I was always disorganised and chaotic. Deeply inappropriate in my teaching methods, and I would bribe my students to learn, with sweets. I was a popular teacher, but not a talented one!’

However not all teachers were so inept, as another of the cast – Konnie Huq, who plays Ms Saeed, recalled her time being taught by Mary Sergent, wife of newsreader John.

‘During sixth form when I was 16, I lied about my age to get my first job in TV, and I said I was unemployed. Mrs Sargent managed to broker a deal between the TV production company and my school, so that I could actually do the TV job alongside my A-levels. 

‘This meant I was a TV presenter while in my second year of A levels, the production company got me a bleeper, when it went off I’d go to the payphone at the school, put in 10p or 20p and then ring the production company office, and they’d tell me who I was going to interview that week. They’d send a cab and I’d go and do it and then come back to school. 

‘I used to film my studio links every Thursday after school and take a change of clothes with me. It was a show called TVFM, and it was on cable and satellite, they had a gap between 5pm and 7pm and decided they wanted to do youth programming, I got the job through an open audition advertised in Time Out magazine. 

‘Mrs Sargent facilitated it all and said, "This will look really good on your university entrance form!"’

• Dexter Procter is available to watch on iPlayer now and will air on BBC One on December 28.