Hampstead Theatre: Curtain up for Act II

Generous lottery funding means that theatre has been mocked of late as a branch of the building industry. Lots of spanking refurbs – from the Royal Court to the Bush, to cite two in London – get more column inches than the work inside them.

Jenny Topper, the artistic director of the Hampstead, the first specially built London theatre (apart from the replica Globe) since the National in 1976, may fuss over the hardware, but her priority is the software – writers and their plays. Her new theatre opens tomorrow, and Topper – who hands over to Anthony Clark in the autumn – hopes her last season will restate the aesthetic values she has promoted for 15 years. "You must put on work you believe in," she says, "but you also have to offer entertainment."

At the prefab hut in Swiss Cottage that had housed the Hampstead since 1962, Topper entertained her local audience with "an eclectic but never boring mix of new plays". She says: "Our average has been 10 shows a year – and more than 40 have gone on to transfer." We're talking serious talent, from Stephen Poliakoff to Jonathan Harvey and Terry Johnson to Alan Plater, with actors such as John Malkovich, Ewan McGregor, Jude Law, Jane Horrocks, Maureen Lipman and Rufus Sewell.

The real turkeys – Michael Frayn's Now You Know or Snoo Wilson's Moonshine – have been scarce. But Topper is not ashamed of her loyalty to writers. They are, after all, part of her theatre's DNA. She's also clear about what she thinks is a good play. "I love the well-made play that is crammed full of ideas and hides its subversive heart in a cloak of laughter."

Purists of cutting-edge new writing – who see well-made plays as naff – may sniff, but Topper is unrepentant. She doesn't like "tiny slices of life or cocky lads' plays". Understandably, she wasn't keen on the way women's voices were marginalised in the in-yer-face 1990s – although the Hampstead staged its share of shock-fests, "mad, bad and dangerous plays" by writers such as Philip Ridley and Brad Fraser.

In its old building, the Hampstead was a fringe venue with the reputation of being a middle-class theatre, staging well-made plays of ideas whose action more often took place in studies and patios than in council estates or bedsits. A Hampstead play is one that appeals to a local audience of intellectuals. It's an unspoken truth that many come from the area's Jewish community.

"That core audience has always been there for me," Topper says. "And the success of the theatre owes much to their loyalty. They have great theatrical instincts and can make or break a show. But actually, I've only put on a handful of Jewish plays."

How will the move into the new building affect programming? "My aim is to aid and abet an even more eclectic body of work." Her first offering, Station House Opera's How to Behave, is a mix of performance, installation, video and tour. "I started my life in theatre when I worked with Lumière & Son," Topper says. "The world of performance art and installations had a real hold on my imagination." Now, in her last season, she's returning to those roots.

Although Topper's ambition is "to put away past notions of what a Hampstead theatre play is", the second play in the opening season, Tim Firth's The Safari Party – directed by Alan Ayckbourn – "epitomises the well-made play", with a clear structure and a dramatic climax. But Topper denies that such entertainment is old hat.

She's also enjoying the freedom offered by her new theatre, with its choice of stage sizes and its flexible seating that can hold between 150 and 325 people. An upcoming play by Tamsin Oglesby has about 16 locations, she says, "so, boy, am I glad that we now have wing space and the ability to fly in scenery".

The new building also allows her to stage Stephen Adly Guirgis's In Arabia, We'd All Be Kings. "It has 12 actors playing 16 characters and we just didn't have enough dressing rooms before." In fact, Topper is as proud of her dressing rooms and loos as she is of the new curving auditorium. Guirgis is American, and Topper has been "hugely encouraged by the sheer energy of American writing in the past two years, despite the collapse of subsidy there in the Clinton decade".

In Britain, however, "we're dealing with a generation that draws its inspiration from television. And that is a terrible place for stage writers to begin." Also, "we live in an extraordinarily cynical and brittle time in this country – cynicism is only matched by sentimentality in being the death of good theatre."

Topper does feel that many young British writers lack ambition. As one of a handful of female artistic directors in theatre, she is conscious that "feisty women make people uncomfortable. In order to be emphatic, women often have to take their voice up a register – and that can sound strident, which unnerves people." She says "people", but I think she means men.

We're talking in one of the new changing rooms, and fiftysomething Topper grimaces at the mirror. "Just look at me," she says, pointing at the wrinkles. "Who is that person? I've been losing sleep since the autumn. It's amazing how vulnerable a big project like this makes you feel."

Strains apart, she's clear about her mission. "You owe it to the writers and public to programme a broad spectrum of work, some of which will appeal to the few, some to the many." As she pauses to wipe away a coffee stain, I'm convinced that both building and plays are in good hands.

Take your seats, please, ladies and gentlemen

There are those who will remember the prefab with a fierce preference: those to whom there was something simply magical about the Hampstead Theatre Club, that feisty one-off with an edgy, anti-West End dynamic. But that's history – at least in terms of site. We may now delete "Club" and prefab, and enter the new Hampstead Theatre, the first freestanding theatrical auditorium to be built in London since the National Theatre 27 years ago.

Designed by Rab Bennetts of Bennetts Associates, Hampstead Theatre has brought a dash of physical drama to London's theatre scene. But we don't experience it immediately: timing is everything.As we approach, we see a building that's essentially a simple modernist box. The main external details – timber slats, glazed panels – are worth a second look, but not necessarily a third. Balanced, well ordered, crisp – these are the words that spring to mind. Martin Richman's light sculptures along the entrance façade give the structure some pizazz at night, but it's all tightly ordered.

But the architectural punchline is worth waiting for. In the lobby, Bennetts has pulled off a coup. Descending three storeys from roof to basement is something resembling a giant zinc cauldron. It is, of course, the shell of the auditorium. And what presence it has: something odd and potent, almost suggesting an industrial process.

Bennetts's concept is instantly engaging, and his treatment of scale and detail is admirable. The way the drum is skewed has been done with a canny eye to the precise development of small tensions between materials, and the relationship of curves and planes.

But this is not shock-tactic architecture. Shapes, trajectories, volumes of space – they all send signals, they tenderise us, psychologically. Hampstead Theatre's cauldron-auditorium does indeed front up the punter for a moment. But then another feeling, pleasurably insidious, replaces the surprise: the cauldron begins to radiate an amalgam of containment and secrecy. You might muse: "Well, I'm going in there." And you realise you're about to enter a glorified pressure-cooker. How apt for a theatre whose history and ethos is to do with staging the new, the unguaranteed, the high-risk.

Indeed, this was a high-risk project. It began with the selection of Bennetts; not because they're a devil-may-care mob (they're prudent modernists), but because they had not designed a theatre before.

There was much more to Bennetts's provisional scheme than the desire to pull off a feat of architecture. He realised it would be an act of bogus bravura to beam down a dramatic chunk of architecture on a more or less nondescript site. So his theatre is part of a wider-ranging masterplan of the urban swathe in which it sits, on the north side of a newly created public space. There will be new development to the south, replacing the old public swimming-pool and library, and obliterating the ghostly footprint of the original prefab.

Audiences will like it because the building – the interior, anyway – is itself a kind of prologue founded on Bennetts's arrangement of key materials – steel, glass, secondary species tropical hardwood, polished concrete, zinc; nothing showy, just a kind of exposed edginess. Most of all, though, they will love the auditorium itself, the cosseting flip side of the zinc sheathing. This canted hemisphere, elegantly slatted with wood, feels right the moment you step inside.

But will the theatre's mix of obduracy and alchemy survive its new poshness? Provocative plays deserve provocative architecture. Jenny Topper can only hope that her extraordinary pressure-cooker becomes London's theatrical hotspot.

'How to Behave' opens tomorrow (020-7722 9301)