In the 1970s we were surprised, albeit pleasantly, by on-stage nudity; today audiences are as likely to be fazed by the actors smoking. The sight of concerned shrink Martin Dysart (Edward Fortes) enjoying late-night cigarettes with horse-blinding teenage patient Alan Strang (Joe Murphy) is as startling now, if less crowd-pulling, than the latter’s full-frontal nocturnal equine frolics.

Times indeed change. Thirty-seven years after its National Theatre premiere Peter Shaffer’s Equus – powerful theatre though it remains – seems rather dated and horribly prolix. Yak, yak and more bloody yak – can no one stop Dysart in his tormented self-denigration and absurd insistence on Strang’s right to self-fulfilment through his ecstatic association with horses?

But this week’s student production at the OFS Studio should be warmly welcomed. The play is a good period piece – gripping, witty and engaging as a why-he-did-it, even as one concludes that Shaffer’s supposed ‘explanation’ for a real-life outrage does not convince in every (any?) detail.

The recent West-End/Broadway revival had the magic wand of Harry Potter (Daniel Radcliffe) waved over it. It might be hoped that this will have helped to earn it a permanent place in the repertoire – an honour that appears to be denied to Shaffer’s (better) The Royal Hunt of the Sun.

Fine performances abound on the OFS stage, chiefly that of Fortes as Dysart, who is rarely off it. Slightly hesitant as he appeared at the start of Tuesday’s opening night – who could not be with so much babbling-brookery ahead? – he went on to deliver an assured and satisfying performance.

Murphy’s Strang, meanwhile, is no less than a tour-de-force, bringing us a tortured adolescent – victim of so much sexual, religious and political bigotry – in whom could be discerned (a happy new feature of the role for me) some prospect of a brighter future. Murphy hopes for a career on the professional stage; on this evidence he seems likely to gain one.

Who could not be impressed, too, by the work of Helen Slaney as the boy’s zealous Christian mother, a woman acutely conscious (like D. H. Lawrence’s mum, also a former schoolteacher) that she has married beneath her, and Tim Kieley as his humourlessly socialist (and, we discover, humourously hypocritical) printer dad?

I also enjoyed (though at times could barely hear) Elizabeth Bichard, as the kindly magistrate who puts Dysart on the case, and James Carroll as the owner of the stables where the horses are so grievously mistreated. Ruby Thomas looks and acts the part well as the horsey and sexually precocious young girl he becomes involved with there – disastrously – but speaks in such strangulated upper-crust tones as almost to require surtitles.

Anna Hextall follows, as surely any director must, John Dexter’s original NT staging, with a central performance area flanked by the entire cast throughout, some sporting the stylised metal heads of the abused horses.

Not the least agreeable feature of Ms Hextall’s approach is that she eschews the presentation of pseudish ‘directorial ideas’ about the play in the programme. Instead, we merely get cast and crew biographies, complete with some rather good jokes.

Until Saturday. Tel: 0844 844 0662 (www.ofsstudio.org.uk).