Simultaneously strong and sad: there aren't many actors who could pull off that tricky combination. Nye, who also writes Men Behaving Badly, explains: "Stella is the person who makes it clear it's a proper office. Sometimes she has to be quite schoolmarmy - and she hates it. That's a paradox in lots of jobs - in politics as well: you do it for the good of the downtrodden, but end up being a downtreader."
Beryl Vertue, the show's producer, takes up the theme. "She has to wield the heavy stick. At the same time, she has not to lose the friendship of the audience. Imelda's got this warmth, so you go with her. You can alienate an audience with a tough character, but she's able to mount that."
Audiences respond well to Staunton because they can empathise with her characterisations - whether it be as the neurotic mother in Kenneth Branagh's film, Peter's Friends, or the frustrated teacher in the sitcom, Up the Garden Path.
"She's really good at quiet acting - I don't know what the technical term for that is," Nye observes. "I relish it when she's doing what I'd describe as British behaviour: not quite managing to say what she means. Imelda's skill lies in being intensely sad, but amusingly so."
For her part, Staunton likes parts with an edge of pathos. All the best comic creations - from Hancock through Basil Fawlty right up to Gary and Tony in Men Behaving Badly - have had an element of the sad git about them.
Sitting at a table amid the neo-classical colonnades of the Kensington Roof Gardens in central London, Staunton nibbles at a plate of seared mackerel and char-grilled vegetables. Looking smart enough to be a solicitor herself in a grey stripey jacket and black skirt, she ventures that "the sadder it is, the funnier it is. Stella takes herself seriously. If she's then made to look a fool, that's funny. Like all those people who have this all-knowing front, you scratch it and it's not there. It's daunting, but it's still a front. It is much needed for Stella's self-esteem, because she's a miserable, lonely, thrice-divorced woman. This job is all she's got - and that's sad."
Now in her late 30s, Staunton has made something of a speciality out of tragi-comedy. According to Vertue, "she can switch from being funny to making you feel sad - all of a sudden. If you're funny, the public won't usually allow you not to be funny. But Imelda can do comedy or drama, and she's one of the few actors the public will allow to slide between the two."
A lively, russet-haired woman given to expansive gestures and accents, Staunton makes for entertaining company. In her work, too, she is partial to the occasional extravagance. "I like it when characters go into a ridiculous realm. Real and truthful is boring. The characters have to veer off - otherwise they might as well just be sitting quietly in the back of a courtroom."
Soon to be seen in Trevor Nunn's film of Twelfth Night, Staunton is currently pre-paring to play Miss Adelaide for the third time in Richard Eyre's revival of Guys and Dolls at the National Theatre. The prospect is inducing mild panic. "I haven't sung for a while," she confesses. "And I keep thinking, 'I'm dancing in fishnets. I've got to get my bottom into shape'."
After that, she hopes to do another series of Is It Legal?. However, she cannot see it following Nye's other hit across the Atlantic. "I don't think it would work in America. It's very English. I mean, where else is quite like Hounslow?"
'Is It Legal?', Thur 8.30pm ITVReuse content