How? The two-word answer is "Tom Stoppard", as the playwright's sprightly upgrade of a screenplay by Marc Norman allows him a new spin on some of his best - and oldest - tricks.As in Rosencrantz and Guildenstern (more than 30 years ago now), Stoppard doodles cheeky marginalia around the edges of Shakespearean lore and legend. His Oscar- tipped spoof-biopic embraces the corniest aspects of cinematic ruff trade and somehow comes through quite unscathed. On the button as ever, Mel Brooks fingered the problem in the subtitle he gave to his burlesque of Robin Hood movies: "Men in Tights".In Shakespeare in Love, his next project after Mrs Brown, John Madden shrewdly plots a way through most of the men-in-tights tangles. The arrival of tubular male legwear in the early 19th century (and, perhaps a bit more plausibly, the advent of photography) marks a decisive breach between ancients and moderns. Could language be the key? Up to a point, but strip out the forsooths and gadzooks from the Flynn-and-Fairbanks era swashbuckler, and it still looks daft.No: I have a theory that silliness ends when trousers begin. A few decades further back, Jane Austen adaptations seldom suffer too much of a credibility gap from their snazzy waistcoats and A-line dresses.

Costume cinema now has to vaccinate its viewers against what Ken Starr might call inappropriate laughter.When, exactly, do our automatic sniggers end? In spite of Judi Dench's balloon-like bathing cozzie and Billy Connolly's kilts, there seemed little intrinsically absurd about John Madden's Mrs Brown. As Kapur's Elizabeth grasped, planned giggles can help suspend our disbelief and forestall too many out-of-place guffaws. Better to cackle at the director's bidding than during that tender love scene or crucial diplomatic crisis. From togas to tiaras, studio-soiled conventions stand between the audience and a proper appreciation of the past like so many sleeping policeman - or rather, laughing policemen. We expect a slice of ham served up with our screen history now. Two generations of gleeful parody - from Up Pompeii and Morecambe and Wise to Blackadder and beyond - have wrapped all costume drama in a swathe of farce that serious intentions (or serious acting) alone can never wish away. For every setting prior to a pretty recent date, history now means high camp.

Indeed, Barbara Windsor herself could hardly have surpassed the Fanny who dipped her flag in enemy gore and rasped at a cringing envoy: "Tell your Eenglish Queen not to send boieez to faaht Maree of Guise." Did these OTT flounces damage the picture? Not a bit. As the French regent Mary of Guise, Fanny Ardant pouted and sneered and heaved to a pitch of bosomy excess that drove an earnest period piece well down the road towards Carry On Up the Tudors. Shekhar Kapur may have picked up a sheaf of warm reviews for his Bollywood-flavoured chronicle of the young Elizabeth, but not many critics dwelt on a bit part that outshone even Eric Cantona's weirdly-vowelled cameo. While it seeks to celebrate one woman's extraordinary gift, its focus is in fact the weird entanglements of her sex life Neither is adequately elucidated.