'You wonder what on earth they are up to'

The improv, fun, and banoffee pie on the set of Outnumbered

Outnumbered returns to BBC One for its fourth series next month, proving that ignoring the well-known adage never to work with children or animals can pay dividends.

But the three children at the centre of the hit sitcom are, famously, treated differently than most child stars. Not given lines to learn or marks to hit, but just given the outline of a scene and asked to improvise around it.

Co-creator Andy Hamliton says: ‘We write the storyline and we write the dialogue, but we try to create an environment where the kids will spin off into something or they'll express themselves in a way that's very individual to them. In most cases, the adults don't get any real warning, and then we step into genuine improvisation.

‘So there is a script, but we never show it to the children and they never learn their lines.’

It was an idea that came from the BBC sitcom Bedtime, in which Andy had written a few scenes for his daughter Isobel, who was seven at the time. ‘Co-star Kevin McNally suggested I didn't show Isobel the script – just give her my thoughts. Isobel customised her lines, and it did look very natural,’ he said.

Hamilton’s co-writer Guy Jenkin added: ‘That made us start thinking about the practical possibilities of getting genuine, realistic looking performances out of young children... You rarely get the feeling that children in sitcoms are real. They tend to be the same type of character – the “smart arse” who says adult things – and they are rooted to the spot, staring at the camera, because they've been told to stand in one place and say the lines. We decided to attempt to do something that hadn't been tried before.’

Knowing that this would be unusual, and possibly difficult to explain to a commissioning editor, Andy and Guy arranged for a sample pilot to be filmed at Guy's house in September 2006. A six-part series was swiftly picked up, but aired in an unusual time slot – 10.35pm, stripped over three nights a week for two weeks. Andy said: ‘It's a good slot to launch new comedy because it's far away from the feeding frenzy of the mainstream slots.’

The pair work by talking a lot, devising storylines. Then one of them writes the first draft and the other reads it, together editing it line by line.

Guy said: ‘I'm sure our families will recognise a lot of the scenarios, but only in as much as they are the kind of things that happen on a daily basis in every home in the country with small children. And because there are two of us writing it, we can always claim the other came up with a specific idea – particularly in the scenes which are about people's partners’

Guy admits that their unique way of filming is ‘a fiendish job for actors’. ‘You've got to be funny, you've got to be real and you've got to respond to what the children do while staying in character,’ he said.

Hugh Dennis says he loved that way of working. ‘It is always a very, very happy shoot and for someone like me who, as a stand-up comedian is used to improvising, it is perfect.

‘We are sitting there with the cameras ready to roll, and Andy and Guy are over in the corner whispering to the children and you wonder what on earth they are up to – which means your reaction is completely spontaneous.’

As a parent of two young children, Freddie and Meg, Hugh says recognises many of the scenarios in Outnumbered: ‘The mum and dad do the classic thing that parents do – try to present a united front, but in the heat of the moment, they find themselves going off on their own and then requiring the other one to support them, however ludicrous it might be.

‘But what makes it really interesting is that there isn't any obvious strain in their relationship. They're clearly very happy as a couple. They might both be making terrible errors, but as neither of them are very judgmental, they're not blaming each other. They're in it together, but they're both a bit rubbish; as are most parents in real life, which makes Outnumbered very realistic.’

Claire, who plays his wife Sue, agreed, saying: ‘Situations like re-loading the dishwasher just after my partner has done it. I think most people are able to relate to those sorts of things. The family gets pushed to the nth degree, and there are some wonderful observations on family life. I think we all found out a lot about each others' marriages and it was quite comforting to know everyone bickers as much as we do about daft things.’

And she, too, said the show was one of the most enjoyable to work on: ‘Being on set is all about ensuring the children don't get bored or fed up. As far as they are concerned, most of the time they are just playing about and having fun. It's great to be surrounded by happy children which makes it a really fun shoot.’

The casting director avoided stage-school talent, instead undertaking a lengthy audition process which involved lots of game playing, determined to find children who would enjoy filming.

Andy said: ‘We try to create an atmosphere on set in which the children can relax and be themselves. Filming comes with a lot of ritual and paraphernalia, and we tried to get rid of as much of that as possible.’

Crew and equipment are kept to a minimum to avoid pressurising them, and a subtle lighting plan has been devised: ’This enables us to follow the action rather than having certain spots where people had to be at certain moments,’ Andy said. And there isn't a make-up artist: ‘Being primped and prodded by a stranger before going on set is one of the things that generates tension.’

Two cameras are also used to record the children's performances, and they always run on the children first, because until they are recorded, no-one knows what they are going to say

Tyger Drew-Honey, now 15, said: ‘The bits that I enjoy most about filming Outnumbered are the people and the food. On set we are all just like a big family. But Oh My God, the food! We have an amazing cook called Pam and every single day we're served delicious meals. My personal favourite is her banoffee pie.’

Daniel Roche, who plays his brother Ben, took five auditions to land the role, which had led to further success, such as playing the lead role in the BBC's Just William

Because of his curtly locks, one of the most popular internet searches regarding Daniel is asking whether he is related to Alan Davies. He is actually the son of the Sun's rugby correspondent Tony Roche.

Over the years Daniel has considered being a forensic palaeontologist, a novelist or a journalist. But he still has a dream acting job: ‘I'd like to play a mad man, a crazed villain, like the Joker in Batman, someone wild. I bet that would be fun. And I think I'd be pretty good at it.’

Ramona Marquez was just five years old when she first appeared in Outnumbered as Karen. She was spotted by Guy's wife at a birthday party, as he explains: ‘She had an interesting personality and was sure of herself without being precocious.’

Perhaps that’s why, when she became the youngest winner of a British Comedy Award in 2009, when she scooped Best Female Comedy Newcomer, shed made one of the shortest ever acceptance speeches, saying only: ‘I just want to say thank you and I am very happy to have the award.’