A Civil Arrangement, Sunday, BBC4 Nuts in May, Sunday BBC4

Alison Steadman is one of those actresses whom it's easy to take for granted. She keeps so busy and gives such dependably professional performances that you can forget that when she is excellent she is really, memorably excellent – and last night, in a BBC4 soiree dedicated to her, we got two such examples, separated by 36 years. Colin Hough's new drama, A Civil Arrangement, was school of Alan Bennett's Talking Heads, a chatty monologue embedded with a twist, featuring Steadman as Isobel, the mother of the bride. We first meet her while she's buying an outfit six weeks before her lesbian daughter's civil ceremony. Isobel herself is unhappily married to Robert, who is having nothing to do with his daughter's big day, being strongly resistant to walking up the aisle to Katy Perry's "I Kissed a Girl".

Isobel, meanwhile, finds a sympathetic ear and free pot plants from her daughter's intended, Janice, who works at a garden centre. "If I was to pick the perfect son-in-law, Janice would be it," she confided, in turn making a same-sex cake decoration by splitting two bride-and-groom cake-toppings and sticking the brides together. Janice appreciated the gesture, and if it was pretty obvious where this was all going – especially after Isobel found herself attracted to Janice's smell ("three fifths Eternity, the rest Baby Bio") – the journey was sweetly believable, and that can only be down to Steadman's reading of Hough's script.

You could, I suppose, argue that A Civil Arrangement dabbled in gay stereotypes – the motorbike-riding girlfriend, the daughter who grew up only interested in reading car maintenance manuals, and so on – but as with everything that didn't directly concern Steadman, this was all background shorthand. It was the words that mattered and these were mostly uncliched (Janice, Isolbel told us, "had sparkling eyes and hands like shovels"), even as it veered, from time to time, towards what you can call Coronation Street whimsy. And does anyone outside this sort of monologue really drink creme de menthe?

They must do, I guess, but then perhaps that was meant as some sort of meta-reference to the world of Abigail's Party. Dating from 1976, the year before that classic Mike Leigh Play for Today, Nuts in May (also written and directed by Leigh, Steadman's husband at the time) had a welcome re-airing last night, reminding me of why I prefer Leigh's television plays to his later films.

Steadman played Candice Marie, the childlike girlfriend of Roger Sloman's anally retentive Keith Pratt, a man who, when not counting the number of times that he chewed his food, iss obsessively planning the next day's menus. Keith's neurotic sense of order extends to the environment – particularly litter and noise – and is set for a collision course with messy reality when the couple book into a Dorset camp site.

Leigh wrote Nuts in May in the same year that John Cleese was penning the first series of his masterpiece, Fawlty Towers, and they have in common the comedy of an uptight man going bonkers when his plans are frustrated. Keith's version of thrashing his car with a tree branch is to hit a fellow camper (after having attempted a citizen's arrest) who has been flouting the rules. And while Sloman was terrific as the easy-to-mock Keith, Steadman's performance as Candice Marie was a brilliant counterweight. She allowed herself to be treated like a four-year-old, as in the scene where she picks up pebbles on the beach, only to be reprimanded that, if everyone took a pebble, there would be none left. It made me realise what an atypical role Candice Marie was for Steadman. Any other of her characters would have rolled their eyes – and no actor rolls their eyes quite like Alison Steadman.