Dinner at Selina Blow's house is a crash course in eccentric bohemian poshness. Blow's Notting Hill Victorian townhouse is all lime walls, startling art, shambolic dogs and wine stains on the antique rugs. Tonight, in anticipation of a small dinner party, the dining room is packed with breathing bottles of red wine (and some rosé 'though it's warm because the fridge is crap'), a huge battered table set with heavy cutlery, chilled soup and candles ('we only dine by candlelight'), a four-year-old called Gus (who is making a car out of an upturned dining chair), and a preposterously glamorous Sri Lankan septuagenarian who turns out to be Helga, Selina's mother. The whole place smells gloriously of slowly roasting beef.

Selina herself is padding barefoot round the kitchen, humming a bit, and watching a Lauren Bacall film on a portable telly. 'Isn't she incredible?' she says. 'She wears a houndstooth suit so well, and those eyebrows! I served her once when I worked in Partridges delicatessen on Sloane Street. I always wanted to work behind the counter but my fingernails were too dirty, so I was put on the till. I nearly got the sack about a hundred times. Oh dear!'

This evening is Selina's second party in 48 hours, (this, despite claiming: 'I'm not naturally social, I'm actually quite shy.') This small dinner for a few friends follows hard on the heels of the birthday party she threw yesterday in her back garden for her three-year-old daughter Violet: 'That was just cake and friends on the lawn, no entertainment or anything. I love eating; basically, I'm very greedy, I think about food all the time. I love giving it, sharing it, the generosity. If I've got a table for four, I'll squash 10 around it, that sort of thing.'

The preparations for this evening are unrolling in a deliciously haphazard fashion. In between admiring Bacall, Blow periodically prods the huge, fantastically aromatic joint of beef which is roasting languidly in the oven. 'It's organic meat. I always get it from our local farm in Gloucestershire. I do like to cook a lot of meat. My brother Amaury likes to cook Edwardian, and my mother is an incredible and very creative cook, but I keep to simple things, meat with a few vegetables, meat I can "stab and stuff things into", which is how my husband describes my cooking style. I'm a rough, instinctive cook. I find too many instructions crush the individuality from a meal. So there's no design to my cooking, no ceremony, it's all about volume and generosity. I like food you can make a midnight feast with later. I don't mind finishing off with a box of After Eights, but really, that's it.'

Selina Blow grew up tasting food of an extreme and varied nature. Helga moved to the Blow family home in Gloucestershire in the Sixties when she married Selina's father, writer and historian Jonathan Blow. She was 17, and missed Sri Lankan cuisine desperately so she began concocting her own curries for her family, after instructing Jonathan to grow wild garlic in the garden, which he did. Selina and her brother Amaury meanwhile, were not adverse to 'stuffing a rabbit with lemons and cooking it over a fire. While everyone else was into fish fingers, our mother liked proper food. She was very interested in Gaylord Hauser's book, Look Younger, Live Longer, it was a big influence on her household.'

The guests begin to arrive, and Selina disappears upstairs to change into one of her own creations - a signature velvet suit in a decadent, deep red. In the drawing room, the outrageously impressive Helga is joined by Dr Charles Levinson, Selina's husband; co-owner of jewellery empire Erickson Beamon, Vicky Sarge; milliner Stephen Jones, and sculptor, artist and jeweller Andrew Logan. They make up a crowd of gently chic, fashionably bespectacled types dressed in the hats and fantastical jewellery which they design, make and sell themselves.

Just before the group sit down to the vichyssoise starter - which, it transpires, Helga made, following her own recipe, a favourite on the menu of her Sri Lankan hotel, Helga's Folly - an ice cream van pulls up outside. It's driven by Morfudd Richards, formerly the maitre d' of the Caprice (where Stephen Jones was a regular), now mistress of Lola's On Ice, an upmarket ice cream company which specialises in bringing freshly made concoctions like Valhrona chocolate sorbet with brandy snap, to dinner parties like Selina's, in a classic refurbished 1970s van. 'I brought it on eBay!' says Morfudd, while doling out 'Pina Colada' (coconut sorbet with pineapple on a stick) to Vicky, who says it's her second ice cream of the day. A couple of Portobello Road's finest 11-year-olds roll up on their BMXs, and start enquiring: 'How much for vanilla, lady?' which makes Helga laugh. 'When I take it out on the streets of Islington, it actually gets quite frightening,' says Morfudd.

Finally, when the ice cream amuse gueules are finished, the group sits down to Selina's meal. After Helga's spiced up vichyssoise, Selina serves big portions of perfectly rare beef with peppery salad and home-made horseradish. Everyone has seconds. Helga regales the table with stories of Helga's Folly and its celebrity guests (The Stereophonics wrote 'Madame Helga' as a tribute to her), and Selina reminisces about holidays spent driving round Italy with Charles. 'He always complains because I make him stop at every deli we pass, and the car gets filled with olives and prosciutto ham. There I am, feet up on the dashboard, munching olives, terribly happy.' The beef is followed by summer fruit and crème fraîche. By an entirely civilised 11 o'clock, things wind down. The guests finish their coffee and call their minicabs. Charles clears plates. And Selina Blow begins to eye up the leftovers, presumably with a view to creating a midnight feast.

· Selina's clothes are available from Selina Blow, 1 Ellis Street, London SW1 (020 7730 2077). For all information on Lola's On Ice go to www.lolasonice.com