In a week when journalistic freedom of speech, and, indeed freedom to mock makes headlines from Paris to Saudi Arabia, it’s a good time to see a play that attacks the legends surrounding that most sacred of cows, Princess Diana.

If, like me, you are an enthusiastic conspiracy theorist – and like a substantial proportion of the audience at Charing Cross Theatre who equally readily raised their disbelieving hands when asked if they thought the incident on the night of 31 August 1997 under the Pont de l’Alma was not a complete accident – you will love this piece for the forensic thoroughness of obsessive Aussie journalist John Morgan on whose nine – count ‘em – books it’s largely based.

If you like a few Now Show style sketches featuring Mohammed Al Fayed, The Queen, James Hewitt or a High Court judge, a constant battering of Piers Morgan, and a delicious sideswipe at Rebekah Brooks, this show is also for you.

The only punters who might be disappointed are her still-living relatives and those Daily Express-reading garage-flowers-strewing shire-dwelling souls who believed her hype and still mourn ‘The People’s Princess’ or think that she did ‘good works’ by going to a hospice at 2a.m with theatrical make-up and a film crew.

Trouble is, Truth Lies Diana is interesting only for the content you might not have heard or have heard and would like to have corroborated: although the event’’s creator and star Jon Conway seems a genial chappie, his play is not a good piece of stagecraft, and neither the uneven narrative nor the sub-plot of a journalist whose wife may or may not be having an affair are well-enough served by the script and the performances.

Conway also plays a convincing if rather too fey Paul Burrell, Diana’s Butler who was also accused of stealing some of her belongings, and Fred Perry is pretty much spot on as James Hewitt admitting he does know who Prince Harry’s father is. Avoiding sketch-show caricature and taking inspiration from the documentary style characters and casting in King Charles III might help in any future staging.

But it’s always good to see the establishment and its lackeys given a bit of a kicking.