Forbidden Broadway, Menier Chocolate Factory, London<br>Ashes, Queen Elizabeth Hall, London

A brilliant, high-speed satire on the commercial theatre takes no prisoners as it lampoons some West End staples

Actors have always poked fun at the foibles of commercial theatre. No doubt it helps them through those gruelling eight shows a week.

Usually, though, they keep their parodies to themselves. It takes a touch of genius to turn them into something saleable, but writer Gerald Alessandrini has that Midas touch. His 1982 revue, Forbidden Broadway, started in a New York supper club, ran for 27 years, and was updated several times. Now a new West End edition has landed. Watch out Andrew Lloyd Webber, Trevor Nunn, Cameron Mackintosh. Be afraid, be very afraid.

An evening-gowned creature simpers into view, her hair a collapsed bird's nest, her lips pulsating jellyfish that she wraps around an outsized mic to squeeze out a Lloyd Webber melody and bewail her ex-wife status. Massive reverb does a kindness to her top notes. You could drive the Israelites through the width of her vibrato. Poor Sarah Brightman. Bravo Sophie-Louise Dann. To bring off so savage a comic assault on a person's vocal technique takes a vastly superior one.

The same performer hits a note of beautifully enunciated condescension as Mary Poppins, using the tune of "Feed the Birds" to analyse the cash-cow formula followed by the Disney Company and producer Cameron Mackintosh. "Feed the 'burbs / Tepid a show / Tepid, vapid, titles they know ..." You wonder whether some people listening might not be offended by this and other aspersions cast on their taste. After all, you've probably only come if you know and love musicals. The night I attend, though, there is delighted, whooping laughter (and it wasn't the press night, either). Thing is, this show lampoons the good, as well as the bad and the ugly.

As always, Forbidden Broadway, directed and choreographed by Phillip George, is performed by just four singers and a pianist – here the tireless Joel Fram. A chief delight is the speed of the show's costume-and-wig changes and the variety of styles and stars that come under fire, the puckish Steven Kynman morphing from Billy Elliot to a coy Daniel Radcliffe in Equus, performing a strip-tease out of his Hogwarts uniform, to Andrew Lloyd Webber cuddling a toy cat which viciously attacks him.

Alvin Colt's costumes are sometimes the nub of the joke, such as when Alasdair Harvey's PR-savvy Cameron Mackintosh flaps his cloak to reveal a lining appliquéd with promotional material for his shows. In a swipe at "Pretty Shitty Bang Bang", the starring car becomes a lusty showgirl (Anna-Jane Casey) with headlamps for breasts, which the rest of the cast enthusiastically polish until they light up.

Not every number hits its mark. Some old favourites are past their sell-by – Liza Minnelli, certainly, and the elaborate Sondheim sequence which has reduced recognition-value for British audiences. But with so much wit and energy to spare, this hardly matters in a show that, even in stifling temperatures with struggling air-con, left you wanting more. What's the betting this Chocolate Factory offering won't make the leap to the West End, like A Little Night Music and La Cage aux Folles before it. It deserves to.

In a week that saw the death, at 68, of the German theatre pioneer Pina Bausch, it seems fitting to include mention of a show that, albeit obliquely, owes much to her legacy. Bausch was called a choreographer, but it wasn't the danced element in her pieces that made them extraordinary. It was her way of exposing hidden layers of the human psyche through speech, movement and stage environment. This critic owes some of the most memorable, most life-asserting moments in 30 years of theatre-going to Bausch.

Ashes, by Belgium's Les Ballets C de la B, pursues its themes by similar means, stripping humanity of its everyday-ness to reveal the raw pain and pleasures bubbling beneath. As so often in this company's bracing work, baroque music, played live and at the highest level, is central. This time it's Handel arias, performed from a scaffold accompanied by strings and theorbo, marimba and accordion – wacky, certainly, but also strangely right, giving a folksy tinge to upbeat numbers and a lugubrious shimmer to laments.

Soprano and counter-tenor direct their songs at the action, as if offering advice to the sprawling, dysfunctional, variously delirious and distressed specimens below: a couple kept apart by a broomstick lodged between them, a duo who act out an entire love affair powered by human breath. Ashes is by turns bewildering, alarming, funny, touching and refreshingly anarchic. A plea to the South Bank: please show it again – for more than two nights.

'Forbidden Broadway': Menier Chocolate Factory, London SE1 (020-7407 4411) to 13 Sep