Well it is the 50th anniversary year of Bertold Brecht’s death, so let’s turn the South Bank of the Thames into the Brecht Bank. The Life of Galileo has already opened at the National Theatre as part of the Travelex £10 Season and now, just downstream, the open-air Scoop amphitheatre, located close to Tower Bridge and nestling beneath the Mayor’s ‘glass testicle’ City Hall building, is presenting The Caucasian Chalk Circle for the summer.

But here you can save that tenner for an interval drink, as the first full-length production since this unique space was opened for public performance four years ago is absolutely free to watch. No need to book either. You simply turn up (maybe with something comfy to sit on; the tiered stone seating can play havoc with your finale) and turn on to an utterly fascinating fable set in a kind of distant folksy Euroland during, as Brecht puts it, “a Golden Age that was almost just”.

The tale of the struggle for possession of an infant son and heir and the sudden reversals of fortune between a governor’s wife, who has deserted the infant during a civil war, and Grusha, the poor servant girl who looks after him in the mountains, is well-told by director Phil Willmott and his troupe of actor-musicians, which even includes some National Youth Theatre apprentice actors.

Emma Stansfield as the maternal Grusha, Joe Fredericks as her soldier boy lover (who has also written the impressive new songs) and Nigel Richards as the rascally judge Azdak, who finally establishes the child’s “real” mother by the chalk circle test, are the lynch-pins providing a strong sense of character and narrative tension.

With lots of al fresco audience interaction, the ensemble climb imaginary mountains, cross bridges, ford streams, swap accents (ranging from broad cockney to bog Irish) and blow their trombones and saxophones to ensure that we keep switching our sympathies. All of this chimes nicely with the Brechtian notion of “complex seeing”; although despite the best efforts of all concerned, his mix of morality and Marxism is in danger of running out of dramatic steam during the second act.

Still, when you are competing with the Heathrow flight-path, the odd passing mobile conversation and the general background chatter of London at dusk, it’s a major achievement to keep a 300-strong audience switched on to a rather abstract play about ordinary people trying to do the right thing under extreme circumstances.

- Roger Foss