Barber, 48, declares her open-plan pad is not suitable now her true love has sailed into port. So the star of Love in a Cold Climate is looking for something cosier.

You realise straightaway that this encounter will be fun. Barber announces she is struggling to write a speech about her time in Antony and Cleopatra. The problem? “I didn’t get on with Antony,” she says. He was played by Nicholas Jones. “I have decided I’ll just talk about previous Cleopatras.”

Barber is a delightful gossip. As the red wine flows she is soon treating me to anecdotes ranging from the writer Edna O’Brien’s tips on how to be dumped with dignity (“never let them see you cry and looking terrible: that will only reassure them they were right”) to what Helena Bonham-Carter said to Gordon Brown: “It was his first Number 11 party and he was so twinkly I came away rather fancying him. Helena said, ‘Why don’t the public see more of your humour?’ ” Brown replied that dealing with the nation’s money is no laughing matter, but identifying the Brown problem shows Bonham-Carter missed a career as a politician.

Barber’s flat is on the market for £1m. First a warning: as soon as you enter the joint you will be sexually assaulted.

Male fans of her fine stage performance in Closer might be deflated to find the culprit is Smack, the resident bulldog. Explain the name please. “I was in a musical by the Pet Shop Boys loosely based on Marianne Faithfull, and I said in it, ‘I’m going to see a man about a dog; a dog called smack.’ ” As said dog attempts to mount your leg (again) you will be relieved to learn he is not included in the fixtures and fittings.

Depending on your taste, this is the grooviest shag pad since Austin Powers. Or a partially converted floor of an NCP car park. So roomy — or empty — is this 1930s flat of about 1,800sq ft in a five-storey former shoe factory that you could zoom around pretending to be Michael Caine in The Italian Job.

“Really it’s just a massive bed-sit,” confesses Barber, revealing rusty estate agency skills, “but it is in a book about lofts.”

Recovering, she reels off its charms — like watching a telly in the seating area while luxuriating in a claw-foot bath. Yep, even the bath is in view of the entire flat: this is a place where only one’s more intimate friends should be to invited to stay.

“It forces you to be tidy,” she admits. “I was messy, but it is depressing coming home to that: you can’t shut a door on it. It has been a good discipline. I did live in a Victorian flat full of bric-a-brac, but I threw it all away.”

When she told the previous owner it lacked cupboards, he asked: “How many clothes can you have?” She replied: “My dear, you have no idea.”

The only private refuge is the loo, a former darkroom, which is reached by a secret door. “When Paul O’Grady came to a party he couldn’t find the loo so threatened to use the corridor.”

So why did she buy the place? “I used to live in a garden flat,” explains Barber, “but five years ago I decided before I got too old and ridiculous I would like a loft. I probably watched too much Sex and the City.” And with the death of her retriever — inherited from ex-boyfriend, fellow actor David Threlfall — she no longer needed the rusticity of Highgate.

Now life has turned full circle. “I have a partner who lives with me mostly and he wants a separate room to do whatever it is he doesn’t want you to see.” She calls him “a proper person, not an actor — he works in corporate videos. We met two years ago through friends”.

The downside of loft living is that when you row “there is nowhere to go”. So she persuaded lover-boy to buy a “bolt hole. I have seen so many relationships go wrong. But I made sure it is only 15 minutes away so if he goes off in a strop — which has happened many times — I can always summon him back.”

So what will she miss? “The fresh air,” she answers breezily; she does not mean that the air is particularly fragrant in EC1, but there sure is a lot of it in this flat. Anything else? “If someone clings on to your legs out of the window, you can see St Paul’s.”

One curiosity is the lack of curtains: isn’t she worried reclining in her bath about the flats opposite? “Oh no,” she says cheerily. “They are illegal immigrants in there too worried about people looking in to look out.”

Barber will never make an estate agent, but she could take up after-dinner speaking. She pours more wine and reveals what Rory Bremner — with whom she appears in Bremner, Bird and Fortune — really makes of Brown (not a lot) to the problem her “big mate” Sir Ian McKellen has with cars: “He worked in theatre and didn’t have much money. His car was so bad that Steven Berkoff gave him an old Mercedes. Even that was terrible: you had to kick open the door.”

She is in gales of laughter about how she saved Christian Slater from Abi Titmuss. “We were having dinner and she sent him messages asking him to Stringfellows. Shameless. I wouldn’t let him go.” The flat is fun; but for a really top time get the agent to throw in the owner — minus the dog.

Frances Barber’s flat is for sale for £1m with Urban Spaces, 020 7251 4000, www.urbanspaces.co.uk

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