Has any other Shakespeare play changed so much in the way it's perceived as The Merchant of Venice? Though most people probably think of it as "the one about Shylock", it's worth remembering that the merchant of the title is Antonio; Shylock is merely part of a subplot in which the hero, seeking to help a friend in need, unwittingly puts himself in the power of an evil and vengeful creature. Fortunately the anti-semitism that was routine in Shakespeare's day is much rarer now, which tends to focus our attention on parts of the play that would have seemed quite unexceptional to its original audience.

Then again, to lay that charge against the play itself (rather than particular characters) is not so straightforward. If Shylock pursues his grudge against Antonio to extremes, Shakespeare goes to great lengths to show why he should feel such hatred for him and for Christian society in general – a lifetime of abuse and contempt, hypocritically set aside the moment a Christian needs his help with the very thing they usually condemn him for, compounded by the loss of his daughter. Moreover, what's the purpose of the "Hath not a Jew eyes?" speech if not to show the absurdity of anti-semitism?

One consequence of this change of perspective is that, as Dan Hannan MEP recently wrote, the trial scene seems to us the play's "natural climax", and it's incongruous to find it followed by "some frippery involving lovers' tricks and a ring". This is evidently the attitude taken by Ricky Dukes, adapting the play for Lazarus Theatre Company's production at the Brockley Jack Theatre, who chooses to end it at this point. He also makes other, more surprising cuts, including Shylock's famous "Hath a dog money?" speech, which I think is a shame as it tells us so much about his history with Antonio.

Moreover, although the programme lists Tracey Pickup as playing Salarino (as well as the Duke, who here becomes a Duchess), Shylock is left to prompt himself with the question of whether he would really take Antonio's flesh if he forfeits the bond, the reason for which decision I don't pretend to understand. The set is a dominated by a large table, with the action taking place on it as well as around it. The box of Shylock's jewels, stolen by Jessica as she elopes with Lorenzo, doubles as the apparently worthless lead casket which Portia's suitors must choose – a nice touch.

This being a Lazarus Theatre Company production, the room is initially filled with acrid smoke, and we are treated to a few minutes of physical theatre before the actual, y'know, Shakespeare gets under way. Once it does, those actors not currently involved in a scene continue to prowl around the edge of the set, which doesn't seem to serve any purpose other than occasionally blocking sightlines and distracting the audience from what's important. The one exception would be Stephen McNeice's Shylock, whose brooding presence in one corner of the stage seems to hang over the action like a pall. Unfortunately he's less effective in the scenes he's actually in, a two-dimensional Shylock without the character's malice or sense of grievance, who fails to involve us in his journey from avenging angel to broken man.

Alexander Shenton is asked to play both Bassanio and his unsuccessful predecessor, the Prince of Morocco. This is another uncomfortable moment in the play, as there's an undeniably racist element to Portia's relief that he chose the wrong casket – "Let all of his complexion choose me so" – and if Shenton thankfully didn't black up or put on a comedy African accent for this scene, I confess I'm not entirely sure what he was doing instead.

Acting honours go to Tracey Pickup as the Duchess/Salarino, Joe Mott as Balthazar/Launcelot and Alexa Reed as Nerissa, a wonderfully natural performance. Ricky Dukes' direction could do with more tonal variation from one scene to another. That said, I must congratulate him for the final moment of Shylock's humiliation, a surprise I don't want to spoil by saying too much here, save that I presume a reference to a more recent anti-semitic persecution was intended.

The Merchant of Venice, at Brockley Jack

Some inexplicable cuts and irrelevant gimmickry can't save a lacklustre Merchant of Venice. At the Brockley Jack Studio Theatre.