Just as anyone finishing a marathon deserves applause whatever their time, so the cast of Man & Superman at the National Theatre would have earned an ovation at the end of three and half hours irrespective of their performances, Ralph Fiennes in particular who seems to have been sprinting the entire way. By reinstating Shaw’s third act set in Hell, director Simon Godwin risks making the occasion a test of endurance for all concerned and it is a compliment to his production that there are only a few, relatively brief longueurs for which the author is mostly to blame.

Fiennes’ energy and command of the text are prodigious. There can be few actors capable of delivering the lines so quickly without sacrificing the sense or losing sight of other aspects of characterisation. To do so over such a sustained period of time calls for Olympian stamina and powers of concentration. He is ably supported by Indira Varma, with whom he conducts a battle of the sexes to rival Beatrice and Benedick; Nicholas Le Provost who, to continue the athletics analogy, comes home first in the seniors’ race; and Tim McMullan as an interchangeable brigand and Devil.

But questions remain about the play itself and its attempted modernisation. The dramatic presentation of intellectual arguments, a field latterly occupied by Tom Stoppard, can make the dialogue sound like an election edition of Question Time, albeit with more appealing candidates on display. There are too few changes of pace to modulate the harangues and although the scenes flit from London via Hades to Granada (a remorseless increase in temperature, as anyone who has been to that part of Spain will know) the characters bat away at each other as if they were still in the drawing room. As for that problematic third act, it is worth seeing for McMullan’s louche Lucifer and gives Shaw openings for some of his sharpest barbs at the expense of the English. But it is easy to see why previous productions have omitted it and let their audiences out in time for a drink after the show.

Then there is the problem of timing in the relationship between John Tanner and Ann. We are asked to believe that they were childhood sweethearts – or rather that the head-to-head scrap between them started young. It is difficult to square this similarity in age with Tanner’s becoming her joint guardian when her father dies. Seeing him as a father figure would fit the psychology of grief if there were more years between them, but that could be passed off as a transitory,  post mortem infatuation. No, Tanner needs to have been fighting with Ann ever since he was a boy and  be guardian material now. Shaw tries to have it both ways but does not quite succeed.

Part of the problem lies in the creation of a strong-willed female lead in her late twenties who, legally at least, is regarded as a child. By 1905 when the play had its premiere that contradiction was starting to wear thin. Put it in modern dress and it sounds ridiculous. Of course the same charge could be levelled at updated productions of Shakespeare in which khaki-clad soldiers, for example, settle their differences with daggers. Somehow the timelessness of the issues and language must avoid being detracted from by attitudes that now appear stuck in the past. This production of Shaw’s brilliant, baggy masterpiece, so magical in many ways, does not quite pull off that most difficult of tricks.