As she raises her voice, passers-by stop and stare. Outside Kensington Tyre Service opposite, a pin-striped commuter briefly halts his route-march home to gawp at the scene, and a stubbly bicycle courier pulls over. By a large Smirnoff billboard nearby, a Chinese couple stop their pram and nudge each other. They could only be watching the filming of a new Victoria Wood.
The difference is that they are not watching As Seen on TV but 'as seen on Screen One'. Pat and Margaret is Wood's long-awaited progression from the three-minute sketch to the 90-minute feature film. The road from Skitville to Movieland is littered with the corpses of over-reaching comedians - Smith and Jones' Morons from Outer Space, or the Comic Strip's The Pope Must Die, anyone?
But Wood fans need fear not: Pat and Margaret contains many lines of vintage Victoria. At one point, the Hollywood actress Pat is approached by two fans on a travolator at Heathrow: 'We wrote to you in LA] We're the two diabetics from Ketteridge]' And - judging from the script - the film is not a three-minute idea tortuously spun out over 90, but a living, breathing feature, with characters rather than caricatures and pathos rather than punchlines.
Taking a breather between shouts at the car-coat (her regular collaborator Duncan Preston), Wood is all too conscious of the dangers of expanding a comedy snack into an eight-course banquet. An earlier draft of the script was rejected by LWT, who told her, 'a film is not a sketch, you know'. But the writer persevered: 'When I had this idea, I thought, 'This is a film, not a sketch or a half-hour play.' You have to be aware that the thread of the story has got to push along for 90 minutes. It can't have what so many films have, a dip at quarter to nine, you know, a 'Shall we go and get some chips?' sort of dip.'
The - resolutely undipping - story centres on the reunion of two long-lost sisters: Pat Bedford, a glamorous LA soap star (a part Julie Walters was born to play), and Margaret Mottershead, a motorway cafe worker and fashion write-off (a part Victoria Wood was born to play). Their relationship develops convincingly from insults - Pat is aghast 'to have a blood relative with a Lancashire accent and a perm you could go Trick or Treating in' - to intimacy, as they find common cause in a battle against a loathsome journalist and an even more loathsome mother. It is not entirely serious - nothing Wood writes could be - but neither does the presence of jokes mean it is entirely throwaway either.
It is the last day of the shoot, and the set is en fete. Filming over, everyone quaffs champagne - 'cheap stuff', Ruth Caleb, the cost-conscious producer, is quick to emphasise - and the director, Gavin Millar, is speechless at receiving from the crew an inflatable 'Oscar for Best Performance in the Role of Confused Proprietor' (because of a tight budget, he has had to play the manager of an old people's home).
In an itchy blue jersey (complete with dernier cri yellow floral patterns on the front) and shapeless beige skirt, Wood is on a high, revelling in the completion of her first full-length work as writer / star. All the problems of location filming are behind her. 'At Heston Services we were ambushed by 45 women on their way to Ladies' Day at Ascot,' she recalls, with a shudder. 'They were all pointing at us as though we were rare llamas in a zoo. And in Blackburn, these ladies came up to the car Julie and I were sitting in and started tapping on the window. 'Eee, are you from Bury? Are you from Accrington? Do you want a brew?' On another occasion, bystanders started videoing us. 'Ooo, it's that woman off telly.' 'Who do you mean?' 'You know.' 'We'll ask Doreen.' 'No, she's in toilet.' '
Wood has a magnetic attraction for such people, whom she imitates out of affection rather than disdain. In particular, women - of all ages and classes - are drawn to the Wood persona, a woman who appears to read the same magazines, watch the same television programmes and visit the same shops as they do. As Caleb puts it: 'She is so popular because she connects with people, she doesn't patronise. Her humour is ordinary - and that's not a derogatory word.'
'I'm just articulating things that they've thought of themselves but haven't put into words,' Wood explains. 'All my comedy is done from a woman's point of view, which doesn't mean that it's not accessible to men, just that it will always have a particular relevance for women. Billy Connolly telling jokes about his willy probably means more to you than to me, but I can still laugh at it.'
Burly technicians come up, air-kiss, and bid fond farewell to Wood. She is in knockabout form, joking about her hairdo from hell - 'no naked flames near it, please, all the budget went on it' - and the problems of body odour on set: 'In one bathroom scene, Gavin said, 'I want you to come in.' I replied, 'I don't think I can.' The smell was like a wall of wool. After that, the smell of chip fat at Heston Services was marvellous.'
In between sips from a plastic cup, Caleb reflects on the pitfalls of comedians 'going straight'. Won't many viewers tune in to Pat and Margaret expecting to see thinly disguised stand-up routines about J-Cloths and Jammy Dodgers, and maybe the odd show-stopping piano number? This is, after all, the comedian who sold out a record-breaking 18 nights at the Royal Albert Hall. Caleb is grateful for the ready-made audience of fans of Wood the stand-up, but contends that viewers will soon forget that and focus on Wood the actress. 'Within five minutes, people won't see Victoria Wood, they'll see Margaret. She completely inhabits the part she plays.' Certainly, in the Acton doorstep scene, Wood not only looked the part, she sounded it, the Lancashire accent coming on strong in moments of anger. In no sense is this a case of a round star being squeezed into a square role. Caleb continues: 'It won't be like David Bowie as Baal.'
In many ways, writing character-based stand-up is the perfect training for writing character-based feature films. In Wood's live act, the beret-clad teenager looking for her friend Kimberley could have come from a movie. Millar, still proudly clutching his 'Oscar', reckons Wood 'has a very good ear for the cliches of common speech. Here she's managed to deepen it into a drama of relationships, a drama of ideas about women's roles.'
So where does Wood collect all these cliches? Does she hang around chip shops picking up dialogue? 'No, but I used to hang around picking up chips,' Wood says. 'I've never sat on buses in the hope of hearing some amazingly Alan Bennett-type conversation. I've just picked up things from my own life. You either have that sort of ear or you don't'
After a break, Wood plans to write another screenplay - maybe for another actor to star in. In the meantime, however, she is hopeful of a cinema release for this one - to follow in the money-spinning footsteps of previous Screen One transfers such as Wide-Eyed and Legless, The Snapper and Enchanted April.
Things have come full circle for Wood, who studied drama at Birmingham University 20-odd years ago. When she started getting work as a singer-cum-stand-up, she gave up her pretensions to 'proper' acting: 'I thought, 'Hang on, I don't look or sound like Ophelia, and I don't want to lose two stone or my northern accent.' '
Wood is not going to give up the day-job yet, but - casting agents take note - she still harbours a desire for straight roles. 'The problem is I don't get any offers. I've got my photo in Spotlight, but not a sniff. I do look barmy in the photo, which could be a bit off-putting. I've got a beret on.'
'Pat and Margaret' will be shown in the BBC 1 'Screen One' season on 11 September