Theatre: It's all lies, cries Barbara Windsor

THE NATIONAL under Trevor Nunn seems to be going through something of an identity crisis. It thinks it's a cinema complex. Over on Screen One, there's Oklahoma! Now the Lyttelton's proscenium arch, which also plays host to Fiona Shaw's larger-than-life Miss Jean Brodie, has been tarted up as the Odeon big-screen that taste never knew: an imposing art- deco facade bathed in an orangey fake-tan glow, framing the ruched curtain of your worst nightmares.

When that curtain rises on Terry Johnson's gag-packed Carry On pastiche Cleo, Camping, Emmanuelle and Dick, we are treated to mock credits, beginning with the full-bodied attack on the trademark Rank gong, followed by a juddering succession of garish celluloid images that abruptly melts in flames. It sets out Johnson's stall nicely - this is both an affectionate, elaborately imitative homage to a landmark of British comedy and a much darker retrospective than you'll ever find at the NFT. What follows represents a successful cross-fertilisation of the surreal celebrity gatherings of Insignificance (Marilyn Monroe and Einstein) or Hysteria (Freud and Dali) and the dissection of Benny Hill-style humour that made Dead Funny so poignantly funny.

The action takes place over 14 years, during the shooting of four of the 29 films, from the apotheosis of Peter Rogers's and Gerald Thomas's end-of-the-pier smut machine, 1964's Cleo, to the creative knacker's yard of 1978's Emmanuelle, after Sid James's death. Although different locations are denoted by backstage projections, the feel is predominantly Carry On Camping, the scenes being almost entirely confined to a cross-section of James's "Merry Traveller" trailer, which hogs the stage throughout with a precarious lumpenness.

The cramped conditions help create a pervading sense of entombed, fetid talent, but Johnson, who directs, has no problem utilising every inch of space for the kind of farcical comings and goings that are his meat and veg (he directed a rompy version of the Restoration comedy The London Cuckolds at the Lyttelton earlier in the year). This is a behind-the-scenes world in which the focus is ever on self-display. Into the nooks and crannies of El Sid's rocking caravan of love are bundled as many women as he can lay his hands on.

Not surprisingly, the trailer rankles with Kenneth Williams, who delivers his opinion the minute he sets a Roman-sandalled foot inside: "I am outraged! This takes the biscuit. And not just any biscuit, I'm talking McVities plain chocolate digestives slightly melted and stuck together in threes." Adam Godley captures the whinnying exuberance and nasal hauteur of Williams perfectly, aided by a script that teems with caustic comments and the kind of fifth-rate double entendres the wag couldn't resist.

Johnson has him locked into hilarious marital bickering with the adulterous, letch-by-rote James (Geoffrey Hutchings, who looks and sounds the spit, down to the croaky laugh and squinty eyes). "You've never suffered the abject, creeping horror of an ailing anus!" the latter is told. No, but he does suffer as intensely as Williams the hollowness of a comic actor running out of time and popular favour. Just as Samantha Spiro's Barbara (so good you wonder whether she is a replicant) can only inspect Williams's anus from afar, so she has to keep her distance from a lover for whom there can be no rescue.

"It's all lies!" I heard the real Barbara Windsor giggle during the opening night. Taken in context, that was a real compliment.

In rep at the Lyttelton Theatre, London, SE1 (0171-452 3000)