Diana’s ghost, Camilla slapping the prince, Kate as Lady Macbeth … people have been outraged by the BBC’s potentially treasonous new drama. But after watching, the response should be more ‘hooray’ than ‘off with their heads!’

Some newspaper coverage ahead of the BBC2 screening of King Charles III – a drama imagining a brief and catastrophic reign for the current Prince of Wales – gave the impression that Lord Hall of Birkenhead, the BBC director-general, should be held in the Tower of London awaiting execution for treason. But the summons he seems more likely to get is to next year’s Bafta TV awards, where the BBC will surely be honoured for one of its boldest drama commissions.

Some Tory politicians and royal biographers had frothed about the content of a piece that includes shots of Elizabeth II’s funeral procession; the ghost of Diana, Princess of Wales, speaking prophecies to her ex-husband and elder son; and Camilla, Duchess of Cornwall, slapping Prince William for plotting to seize the throne from his father. The objectors hadn’t seen the original play but considered even the idea lese-majesty.

'Distasteful': BBC's King Charles III sparks anger even before it is aired Read more

Those not calling for the DG’s head were perhaps aware that the script had not been hatched by a bunch of crazed republicans in a Broadcasting House bunker. King Charles III is an adaptation of a stage play by Mike Bartlett already performed around 400 times in London and New York, transferring to the West End and Broadway after its premiere at the Almeida theatre in north London in 2014.

Such moments as Camilla’s slap and Diana’s ghost – white-dressed at the end of a long corridor beside an eerily rocking child’s rocking horse – will inevitably have caused more shock on TV, where it is easier for the potentially offended to stumble on the stuff, than in the theatre, where the response was standing ovations and award nominations.

However, TV viewers have now seen that the play is not an exercise in Spitting Image-style satire: the actors sample some mannerisms from their Windsor originals, but give imaginative portrayals, rather than Bremner-esque impressions.

Nor could the script ever be mistaken for a docudrama. King Charles III is a futuristic what-if – set in around 2022 – which becomes a political thriller, a Palace of Cards if you will, when the new monarch refuses to sign a parliamentary bill he dislikes, causing a constitutional crisis and civil unrest. Distanced not only by time but style, it is written in blank verse, Bartlett’s governing conceit being that Shakespeare had survived to characterise Charles III as he did the various Richards and Henrys.

Facebook Twitter Pinterest Tim Pigott-Smith’s performance avoids any trace of the pettiness, temper and self-indulgence attributed to Charles by biographers. Photograph: Robert Viglasky/BBC/Drama Republic

Conceived as a pastiche of dramatic tragedy, the play now trails a real one, in the sudden death last month of Tim Pigott-Smith, who played the title role on stage and screen and whose performance now becomes his memorial.

Pigott-Smith’s performance and Bartlett’s script avoid any trace of the pettiness, temper and self-indulgence attributed to Charles by biographers, offering a plausible emotive portrait of a man who has waited more than 70 years to start work, then finds himself incapable of being just a face on the stamps and banknotes. “What am I?,” Charles asks, a line that Pigott-Smith, with an agonised sigh, makes as existentially heart-wrenching as Hamlet’s To be, or not to be.

Even the constitutional crisis Charles provokes is a kindly choice. Bartlett doesn’t imagine him leading a military dictatorship or massacring modernist architects, but standing up for the freedom of the press (something that has never seemed high on the agenda of the real Prince of Wales).

And, in one sense, the play is optimistic and reassuring for monarchists. The coronation oath taken here makes the King of England monarch of territories still including Scotland, Northern Ireland, Wales, Australia, New Zealand and Canada, which only a plucky royalist would bet their Buckingham Palace garden party ticket on at this point.

Much of the play has been cut – the 90-minute TV slot is an hour shorter than the theatrical playing time – and some of the excisions make the text less challenging to BBC editorial guidelines. Rupert Goold, who directed the play in both media, admitted in an interview that the broadcaster had expressed unease with Diana’s ghost mocking Prince Charles’s suitability to rule. That speech has gone.

Electioneering politicians may be relieved as well that a speech from the play in which a kebab-seller laments the shrinking of Britain (“cut the army … squeeze the NHS … the Post Office closed … Devolution. Less and less”) becomes on TV a metaphor in which the Queen holds the UK together like the metal spit that splits a turning slab of doner meat.

Parts of the play are genuinely shocking, with the attitude of viewers depending on whether they believe living royals should be protected from fictional representation (as they effectively were in Britain until the 1980s), or conclude that inclusion in a drama can be no worse than the intrusions into their privacy the Windsors suffer regularly.

Facebook Twitter Pinterest Bartlett gave his Prince Harry a romance with a sparky outsider, played by Tamara Lawrance, long before the real Harry’s relationship with Meghan Markle. Photograph: Robert Viglasky/BBC/Drama Republic

One pre-transmission furore concerned a line in which a nightclubber repeats gossip about Prince Harry’s paternity. But, in the context, this claim is spoken by a committed republican, who subsequently recants, and clearly represents the sort of stuff the princes have to put up with. Richard Goulding’s vulnerable, touching Harry seems a fair guess about the psyche of the fifth in line to the throne. Bartlett also gave his prince a romance with a sparky outsider, played by Tamara Lawrance, long before the real Harry’s relationship with Meghan Markle.

The appearance of Diana’s ghost, as well as being a nod to Shakespearean convention, also seems a reasonable presentation of the way Charles, William and Harry are shadowed by the dead princess both historically and, as her sons have acknowledged in frank interviews, psychologically.

Whether or not you believe that William and Catherine would ever, like Cambridge Macbeths, mount a palace coup, Oliver Chris and Charlotte Riley are completely convincing in suggesting how such a conflict of loyalties would play out within the family.

King Charles III, on TV, is two different things: an outrage for those who believe the monarchy should always be reverenced, especially by the BBC, but also a drama with the highest quality of acting, writing and filming. Strangely, those versions sometimes co-exist: a paper whose front page railed against the BBC for questioning Prince Harry’s DNA gave the play a five-star preview on its TV pages on the same day.