After the grand opening of the Rose in Kingston a month ago, I went back to have a look at the theatre itself. I'm all in favour of legroom but this was ridiculous. The pit in front of the stage where "groundlings" pay £5 to sit on cushions was so sparsely occupied I could have lain down in it and even rolled around a bit.

The stalls benches, admirably widely spaced, were also occupied by only a scattering of theatregoers, but it was the pit I noticed. With fewer than 10 people sat in the yawning space between seats and stage it made the theatre seem - well, empty.

The Rose is not beautiful - its vaguely corporate exterior hints at its conception as part of a 1980s riverside apartment development - but it is very user-friendly. There are lots of roomy bars, lots of loos, lots of natural light.

The interiors are pleasingly unfinished, which chimes neatly with these austere times, as well as matching the unpretentiously bare auditorium and stage. But naked space becomes a negative rather than a positive attribute when a theatre can't attract enough friendly users to make an impression on, let alone fill, its 900 seats.

There were good arguments for finishing the Rose. The shell was there. Its lozenge-shaped stage and horseshoe auditorium make it a unique space. It only cost £6 million (compared, as Hall pointed out to me, to the £100 million for the new RSC theatres in Stratford). It has a potentially big local audience. Yet it will still need funding, or a miracle, to survive.

Cameron Mackintosh also believes there are good commercial reasons for building the studio-sized Sondheim Theatre between the Queens and the Gielgud on Shaftesbury Avenue, arguing that it plugs a West End gap, enabling smaller productions to transfer from the Donmar or Almeida. Fair enough. But after that, might I suggest a moratorium on new theatres in London?

The West End playhouses are falling down. Several new or rebuilt theatres - Soho, Hampstead - have struggled before finding an audience and an identity. The Cockpit and the Cochrane have been returned to educational use augmented by private hire. We are in a halcyon period of theatre, but the amount of good work around, and the London audience prepared to pay to see it, is not infinite.

Nor is the funding necessary to keep our culture vibrant, as the recent threat to the Bush Theatre showed. It's time we thought about how best to conserve or creatively use our existing stock of theatres, rather than further adding to it.

• Blonde Bombshells of 1943 opens tonight at the Rose (0871 230 1552, www.rosetheatrekingston. org) and runs for three nights. The Tempest opens on 25 February.