Le Cirque Invisible, Queen Elizabeth Hall, London

It's amazing to think that Le Cirque Invisible is 40 years old, that is, if you include its first incarnation as Le Cirque Bonjour, then as Le Cirque Imaginaire. A family business, headed by Jean Baptiste Thierrée and Victoria Chaplin, daughter of Charlie Chaplin, it used to include the couple's two children, James and Amélie, who are now carving out independent performing careers.

Le Cirque started as part of the "new circus" movement: no working lions, humiliated in cages, no elephants. Instead there is a crowd of undisciplined ducks who, in the words of the inimitable Thierrée, "between tours return to a farm where they never get eaten". There is also a handful of placid rabbits, who are given books to read in case they get bored, a few doves and three invisible fish. The latter, being invisible, only exist as one of Thierrée's optical jokes.

The Cirque Invisible is fortunately very visible, returning to the Queen Elizabeth Hall, as last summer, a work-in-progress that has evolved over the decades along with its spectators, some of whom first came as children and now bring children of their own. Several of the jokes have been around for a long time – Thierrée's suitcases and matching outfits in zebra or tapestry patterns, his search for missing fingers in a pile of chopped carrots – but I could see them again and again and still burst out laughing.

It is equally amazing to think that Thierrée is now 73, unruly hair completely white. The rest of him, though, is unchanged, as is Victoria, nudging 60 and looking half that, with her long, child-like hair, wide-open eyes and elfin body.

They both offer their separate forms of magic. Victoria, an acrobat, performs on the tightrope with an old-fashioned, nostalgic charm as well as a refined technique. She is also the master of extraordinary transformations, reinventing herself into strange baroque creatures that mutate out of assorted lengths of cloth, parasols and fans. An 18th-century panniered countess reassembles herself into an extra-terrestrial horse, its head shaped out of the dress's bodice; a doll-like creature, moving as though on ball-bearings, becomes a giant mollusc; and a table, with teacups and saucers, somehow morphs into a smoke-billowing dragon.

Thierrée is the jester, with his opera-singing knees, collapsible wine bottles and hair frozen into a sideways billow by a silent wind, along with his ice-cream cone. His conjuring tricks have a Tommy Cooper helplessness about them, the punch-line sabotaged or their secret mechanism revealed.

Everything about sawing-the-woman-in-half works fine – until the end with its unforeseen and perplexing result. But when the tricks do succeed they come as an enchanting surprise, all the more appealing for their gentle playfulness.

Jean-Baptiste Thierrée and Victoria Chaplin remain free spirits of extraordinary, unique inventiveness. Out of humble everyday objects, they create a world of poetry and humour that manages to be both surreal and life enhancing.

If you are feeling depressed and your doctor offers you tablets, I would start by giving Le Cirque Invisible a try instead.

Le Cirque Invisible (0871 663 2500), to 25 Aug