Time wreaks curious changes. Matheson is now the executive producer of Screen One and, as such, part of the new BBC, painfully evolving under John Birt. She would probably rather smuggle herself out now than confide in a journalist.
You can pry and probe around her perimeter for hours, yet still not draw the faintest hint of a criticism of the corporation, of the producer choice funding system, of the quality of drama or even the quality of the tea in the BBC canteen.
It is easy to understand this. First, Matheson is in charge of one of the BBC's most important and prestigious slots, spending up to pounds 1m on each production. Secondly, her overall boss, Charles Denton, was appointed with the specific task of extending the Birt revolution to the drama department. She is therefore unlikely to be found waxing lyrical about the dear, dead days of the 1970s.
Thirdly, and most sensitively, she is doing the job at the same time as continuing her former career as an independent producer. Small wonder that Matheson's law of diplomatic reticence also extends to any criticism of ITV. After all, next week she may have to be negotiating with them.
She insists, though, that nothing has changed.
'If the BBC said to me: 'We're not going to commission this programme,', I'd have the journalists in in a trice,' she insists. 'But I've not been cowering in Television Centre afraid to commission things I think are interesting. The channel controllers want challenging stuff and I don't have any sense of me, or anyone else, being restrained. The films I've commissioned for Screen One are no less interesting than the plays I commissioned for Play for Today. I think it's a romantic idea that everything I did for Play for Today was cutting edge, I'd describe it more as shambolic.'
Tall and athletic-looking, Matheson, 47, has a strong, confident exterior. She lives at the smart end of Vauxhall, south London, with her three sons (including 11-year-old twins) by her former husband the playwright David Hare - another subject on which total discretion is maintained. But despite her caution, she is seen as a free spirit.
'She's like a bird of passage,' says one BBC producer who knows her well. 'She doesn't want to be a permanent BBC person. She's just passing through.' Matheson, who joined the corporation last November, is contracted to run Screen One for just one more year and will spend part of that in Japan, executive producing James Clavell's novel Gai-Jin as a mini-series for the American network NBC.
Over the past decade, she has given up one high-executive job after another. She was controller of drama at Central, where she confirmed her reputation as a backer of hard-hitting drama with award-winning plays like David Leland's Made in Britain, then (with Denton) went on to found Zenith Productions, where she was responsible for some of the most successful British films of the Eighties - Personal Services, Wish You Were Here and Prick Up Your Ears among them.
In 1990 she joined Tony Garnett to run Island World Productions, the independent behind such BBC hits as Between the Lines and Cardiac Arrest. She left last year after the company decided not to develop feature films in Britain.
She was mentioned in the press as a possible successor to Alan Yentob as the head of BBC2, but insists she was never knowingly a candidate. 'I wouldn't be good at it,' she says. But surely she could rise that high in the hierarchy of British television?
'Your statement reflects a view of the hierarchy I don't share,' she counters. 'Lots of cars and carpets and curtains - to my mind, that's not necessarily rising high, it's just a way of carrying on.
'I am ambitious, but it depends to do what. In fact, I'm ambitious to do good work. But you can't put that - it sounds ridiculous.'
She takes over Screen One, from executive producer Richard Broke, at a time when - unlike much of the BBCs drama output - it has actually been doing rather well. Last year's films - like Jack Rosenthal's Wide Eyed and Legless (of which Matheson was executive producer) and Roy Clarke's Foreign Field with Sir Alec Guinness - were well received by both the critics and audience. Broke has apparently never been given a full explanation as to why he was being relieved of his post.
'It was a case of new brooms.' Matheson says, bluntly. 'New people came into the drama department and they wanted to make changes. But I do think that, with something as important as Screen One, it's right that the baton should be passed into new hands from time to time.'
A Breed of Heroes, which opened the season on Sunday, (attracting a modest estimated 2.4 million viewers), was produced not by Matheson but by BBC Northern Ireland, to tie in with the BBC's current season on the Troubles. Insiders expect the six films chosen by Matheson to be a little less cosy than last year's. But there is also a strong sense of the commercial - in next Sunday's comedy Pat and Margaret with Victoria Wood and in the casting of stars such as Richard Harris, and Elliott Gould.
Nor is controversy likely to be absent. The film Two Golden Balls, produced by Matheson through her own production company (her deal with the BBC gives her the right to make one such production a year), is a strong piece about women and pornography which had been turned down by the BBC's head of serials, Michael Wearing.
Matheson admits that television drama has become more predictable, but hopes this season will do something to reverse that trend. 'I've been guided by what I like to watch, and I like to be surprised, amused, stirred and provoked.' And entertained? 'Funny I didn't mention that. I remember in one of the first interviews I ever gave, I said I had one prime ambition - not to bore the audience. I don't think that's changed.'