Paul Whitehouse on his new show Nurse

At a press conference to launch his new bittersweet comedy, Nurse, Paul Whitehouse lets slip that he's had stents fitted to his arteries to help blood flow.

'I've got three stents, four kids, five Baftas,' the 56-year-old jokes. 'There are things in the world that make me anxious, but I don't worry about illness. I worry much more about mental illness than physical illness…'

Mental illness is the topic of Nurse, based on his Radio 4 series of the same name, and covering the encounters between a community mental health visitor and the patients she sees on her rounds.

It might not be an immediately obvious topic for comedy, especially if the aim is to treat the subject with sensitivity.

Not that Whitehouse sees any difficulties: 'In any field where there's profession involvement and tragedy there's always humour - call it gallows humour or whatever – but there always is. So I don't think we're doing anything that could be construed as laughing AT those people, because I think there's humour in every walk of life.

'Also you can't go out of a character in order to do a joke and crowbar it in. For a start it wouldn't sit happily with the subject matter. It is bitter-sweet; the darker tragedy is not hilariously funny but it has its own humorous element to it.

'I don't think we ever wrote anything when we thought, "Ooh, you can't say that'". You're always not self-censoring but you are always you're own sternest critic. So we would have been very conscious of not crowbarring stuff in.

But he adds: 'I don't think it [mental health] is a taboo subject any more, actually. So many people have been touched by Alzheimer's, especially, because people are living longer. Every family has and to deal with these issues and it is bing talked about more. But I still think you have to deal with it sympathetically.'

Characters Whitehouse plays include the 'ageing rake' Herbert, who has a penchant for quoting Yeats and Dylan Thomas; agoraphobic criminal Billy who has become institutionalised by prison; manic-depresses Seventies rock star Ray; and morbidly obese Graham Downes, who first appeared on Whitehouse's show Down The Line,and has an unhealthy co-dependency with his feeder mother.

Whitehouse says that originally the plan was for the show to feature just one character 'an old actor who's starting to fall into the grip of Alzheimer's' but 'I just felt it was a little restricting, a bit dull, because I get a bit bored playing one character so I thought, "We're missing a trick here" we should spread it out bait to discuss other things than just Alzheimer's

'We' – that's him and co-writer David Cummings – 'just sat down and thought we could do something with a lot more variety and even incorporate creatures called women.

'Although it is nominally about mental illness is is about all sorts of subjects. Herbert talks about loss of love more than anything. Now he's come to the end of his life, what is the point of life other than death? So there's subjects that affect all of us really.

'The relationship between Liz [the nurse, played by Esther Coles] and the service user, to use the jargon, just allows them to talk about deep-rooted issues that affect everyone. Whether they need treatment or not is almost irrelevant at times.'

Other patients include barely mobile 'cat woman' April, ex-soldier Jack with post-traumatic stress disorder, and Lorrie, a devout Christian forever bugged by her interfering elderly Jewish neighbour Maurice, who Whitehouse does play.

'What we've found in the discussions with the practitioners is that a lot problems are unhelpful neighbours or family members. They get slightly envious of the attention the mental health nurse gives, so they try to hijack the situation, so it probably displays the need we all have for a bit of attention… and of course some drugs.'

Although Whitehouse and Cummings did check with mental health professionals on some aspects of he scripts, they made a point of not doing too much research.

'We wanted to make sure we were as authentic as we could be, but with our writing process I tend to think a lot of research gets in the way,' Cummings says.

'Our writing process is extremely slapdash; we're not very disciplined. With some characters like Graham Downes, Paul largely improvises a lot of the dialogue on the spot and I'm desperately trying to keep up on the laptop.'

Whitehouse - who jokes that their writing sessions largely involved 'slagging other comedians off for a couple of hours' – adds: 'We were also aware we didn't want to be associated with any particular organisation… often they are specific to one area of mental health, and we are broader.'

He also reveals a very specific inspiration for the role of forgotten rock star Ray – The Troggs, and specifically the tapes of their intra-band rows.

'Dave and I have used the Troggs in everything we've done for years,' he says. 'but we've hidden it. This time we have shamelessly plundered it.'

Performing the diverse roles also required quite a bit of 'hot, heavy and itchy' prosthetics – especially for the dangerously overweight Graham… which is when Whitehouse revealed his health issues.

'We did film it in the middle of the summer, and I was wearing all that gear,' he says. 'I'm not going to bang on about it, but I've got a few stents! I don't think my doctor would have been very pleased with this whole process. I was toying with heart failure. But that's how I like to roll…'

But getting into the voice of the characters was easier. 'I've been doing it for so long – all my life really – that getting in and out of character, I don't have to go and agonise Method-ly for hours on end. I've always been able to that.'

Despite Whitehouse's joking, Nurse represents a much more weighty turn in his work. 'It's an adult format where you can examine very serious issues,' he agrees.

'It was joy to do characters with real depth and meaning. Graham Downes, on Down The Line he's just a one-dimensional character with weight issues, and we just wanted to push it on a bit.

'I still love doing stuff with Harry, more knockabout comedy, I love that. We did The Story Of The Twos and it's probably one of my favourite things. Harry and I might celebrate our own anniversary next. We've been together for 25 years so it's a possibility that we might be doing something with the BBC.

'I was with Harry yesterday, he's slightly jealous of Nurse, slightly jealous of Aviva, but I'm keeping it. He's hoping I drop dead and he can take over the Aviva campaign…

He's very gracious, Harry, he always was - even about the Fast Show – very successful though gritted teeth.

'But it's lovely to do something with more weighty issues too, so I hope to still be able to do more knockabout character comedy. I'm lucky really, that I can do the two.'

• Nurse starts on BBC Two on March 10.

Published: 2 Mar 2015