1968 – what a momentous year for British theatre. The new Theatres Act did away with the censorship by the Lord Chamberlain’s office and writers now the freedom to convey the characters, the stories, and the satire that they had previously had to employ subterfuge to produce – that is, if they could produce it at all. Watching this revival of Peter Barnes’ savage 1968 comedy The Ruling Class really brings back that atmosphere of challenging the system, daring to be different, taking risks that might or might not work, heaping anarchy on to the stage; having pure expression as your dramatic be-all and end-all.

There’s no way this play would have been passed by the censor without his blue pen scrawled all over it. The main character spends much of Act One hopping on and off a crucifix (he thinks he’s God by the way, so it’s not inappropriate). The censor’s guidelines that had been handed down since 1909 included a clause that a play should not “do violence to the sentiment of religious reverence”. Well this play does that quite a lot. The 14th Earl of Gurney’s justification for believing he is God – “when I pray to Him I find I’m talking to myself” – is a pretty damning slap down to any fervent Christian.

But that’s all history now. In 2015 we take it for granted that we can say or do what we like on stage (more or less – there’s always a chance that a Mrs Whitehouse-type person could bring a private prosecution, mind) and as such, for the most part, we don’t tend to push the boundaries that much anymore. It’s already been done, and we frequently take that as an excuse simply not to bother with it nowadays. But back in 1968, boundaries were there to be dismantled. The title itself – The Ruling Class – makes no apologies for its black and white vision of the nobility; a simple tale of old Tory folk, representative of many who basically ran the country.

There’s the traditional family elder who likes to put on a tutu and dangle from a noose, the wet behind the ears toffee nosed cousin destined to be the local MP, the husband and wife who each take lovers as a given right, the mistress who can be employed to marry the Earl just so she can bear an heir, and of course the Earl himself, hidden away for years but who returns to take on the mantle of family leadership, despite being a paranoid schizophrenic who believes he’s God. At least he’s God until the second act, when he starts believing he’s something far more sinister. Outwardly the face of respectability, the play assumes that the Gurney family are typical of the old landed nobility on which the country has relied for centuries, and to whom, in previous decades, dramatists might have handled with kid gloves and loving respect. Not so Peter Barnes, who sideswipes the traditions and reveals the Earl and his family to be the immoral horde of crooks, lunatics and perverts that they are.

So is this play relevant today? Given the fact that we still have a considerable class structure, that a mere 1% of the world’s population own 48% of its wealth, and that you still have to have a considerable degree of independent wealth in order to stand for parliament, I’d say yes. Added to that the continued debate about the value of the House of Lords, questions of espionage, and a still inadequate understanding of mental health issues, and this is as relevant as ever. The only way in which the play feels at all dated is in some of the references. Old retainer Tucker goes loco on the news he will inherit £20,000, which at today’s rate would be about a quarter of a million pounds – currently about half the cost of the measliest studio apartment in Chelsea. The musical numbers, that the cast occasionally break into with delightful 60s anarchy, nobody sings anymore. “Dem dry bones” “My Blue Heaven” and the Eton Boating Song definitely represent a different era. Personally, I don’t think that matters much. It was written in 1968 – and it’s set in 1968. Not everything has to be today.

Jack’s second act transformation from benign (if loopy) God to Jack the Ripper also highlights one of the time’s major obsessions. I can remember the Dowager Mrs Chrisparkle saying there were only two things she hoped would be revealed before she died – proof that the Loch Ness Monster exists (yes, I know) and the true identity of Jack the Ripper. I don’t think either of those mysteries quite captures the imagination of the public today in the way that they did in the 1960s. A modern audience member who hasn’t done their research or bought the programme might well be confused by Jack’s identity change in Act Two, and if you don’t recognise the names of the Ripper victims as they get called out, you might not realise which way the play’s going. However, in 1968 those names would have been instantly recognisable by the entire audience. Of course, many of the Ripper theories suggest that a member of the nobility might have been responsible for the murders, so moving the plot in this direction not only gives it a nice twist but is still in keeping with exploring the reprehensible kind of tricks a family like the Gurneys could have up their sleeve.

Jamie Lloyd’s production is fairly faithful to the original, although I enjoyed the joke of having two male actors playing the Tory ladies Mrs Treadwell and Mrs Piggot-Jones. With a central role like Jack Gurney, it’s easy to see why it attracts larger than life, charismatic actors like Peter O’Toole, who took the role in the 1972 film and flung his unique magic at it. Now one of our best young actors, James McAvoy, has taken the reins and gives us a really entertaining and credible performance. It would be easy to go over-the-top with this role and make the character into a flamboyant show-off, a mere figure of fun whose eccentricities are there for us to laugh at and ridicule. But like King Lear’s Fool, there’s much more substance to Jack, and by making him a considered, rounded sort of paranoid schizophrenic, it makes his second act development not only perfectly reasonable but also very sinister. Mr McAvoy has great stage presence and excellent comic timing but is also scarily serious when the text calls for it. I’m pleased to report he also gives a graciously happy curtain call.

He’s supported by a talented team who provide us with some excellent performances. It’s been many years since I’ve seen Ron Cook on stage and I’d forgotten what a great actor he is. His Sir Charles Gurney is a delightfully weasly, self-centred, horrid little man, trying to maintain as much power for himself by manipulating those around him. Serena Evans, as his wife Claire, is a perfect match for him, weighing up how do you solve a problem like Jack with seeming innocence, but when she goes in for the kill it’s not quite the kill she expected. Her performance is a classic mix of nobility and tart. Kathryn Drysdale is nicely duplicitous as Grace, the 13th earl’s enamorata, Sir Charles’ mistress and the 14th earl’s wife. She’s in it for what she can get but at the same time shows a surprising loyalty towards her husband. Noblesse obliges for her just as much as anyone. Joshua McGuire, a fantastic Mozart in last year’s Amadeus at Chichester, is perfect as the simpering cousin Dinsdale, a typical Lord Muck character, acting superior whilst being completely lacking in substance; and I also enjoyed the quiet dignity of Elliot Levey’s Dr Herder, seemingly authoritative in his medical knowledge but joining the list of stage psychiatrists who end up on the off-piste side of the mental sticky slope in strait jackets. Joe Orton, who also combines lunatics and doctors in What The Butler Saw, would have loved the idea of the doctor being sexually aroused by a detective’s dead body outline on the floor.

Anthony O’Donnell provides many of the best laughs with his aggressively irreverent manservant Tucker, puffing away on his cigar as he joins the big league, but whilst also confiding in us that he is a Soviet spy – and why not? In Mr Barnes’ world nothing can be taken for granted. Michael Cronin is a pompous windbag of a Bishop, and Paul Leonard and Forbes Masson give excellent support in a variety of minor roles, including the ghastly Tory ladies, and I really liked Mr Masson as fellow Old Etonian Truscott, showing that the Old Boys Network is a solid bond that mere insanity cannot break.

So although it’s very much of its time, this play also reveals timeless truths about timeless issues. A very funny production of a remarkable piece of writing, full of the joy of late 60s freedom and anarchy. A welcome arrival in the West End – we both loved it.