When Duncan, the doomed King of Scotland in Shakespeare’s Macbeth, despairs that “there’s no art to find the mind’s construction in the face”, he is citing ancient wisdom. Yet perhaps because the evil characters in fairy tales are ugly and the good ones all handsome or beautiful, most of us tend to grow up believing that external beauty is a reflection of internal loveliness. This is a forgivable error, not least because the very good looking do have an easier row to hoe and can often afford to be nicer and more generous human beings.

Moreover, as people hit middle age, their faces really can reflect the person within, if only because habitual expressions leave a permanent mark in laugh lines or a turned-down mouth.

Oscar Wilde’s only novel, The Picture of Dorian Gray, is about a spectacularly beautiful young man who embarks on a long career of corruption and viciousness, but whose face never reveals any trace of his evil ways. Nor does he age, thanks to a satanic bargain whereby all the ugliness that his face should show appears instead on a portrait he keeps locked away in an attack.

Gray is classic gothic horror fiction in the tradition of Dr Jekyll and Mr Hyde and the works of Edgar Allen Poe, though it is also interesting for its homosexual subtexts, and a rather confused moral message. This latest film adaptation of the novel tries to stress the horror elements of Wilde’s tale, exploiting the full modern armoury of computer-generated effects. Not only does the hidden portrait start to show a red-eyed and aging face, maggots crawl out of the canvas and eventually it starts to make loud, scary growling noises.

Directed by Oliver Parker, the British director responsible for the crude 2007 remake of St Trinians and a ham-fisted 2002 adaptation of The Importance of Being Earnest, starring a mumbling Rupert Everett, Dorian Gray is one of those films that adds modern “edge” to material that does not benefit from such improvement. All too predictably it expends much energy in self-conscious and heavy-handed depictions of the degraded underside of Victorian England, including some unintentionally comical orgy scenes.

Worse, it changes the ending of the book in a way that misses the point of the story (and that Wilde would have despised), and the film’s excellently designed costumes and interiors clash awkwardly with dialogue by screenwriter Toby Finlay that is spattered with anachronisms, prompting men in frock coats to say things like “wow” and “I thought it would be fun”.

Dorian Gray is played by Ben Barnes who looks strikingly like Keanu Reeves but walks with a lolloping oafish gait that looks out of place in an elegant London salon. Lord Henry Wooten — here mysteriously deprived of his title — is superbly incarnated by Colin Firth.

It is Wooten who corrupts Gray, encouraging him to search endlessly for new sensations, regardless of the cost to others, and to “burn with a hard, gem-like flame” (actually a quote from the writer Walter Pater who inspired so much of the “Aesthetic Movement” of late Victorian England).

Ben Chaplin is Basil Hallward, the painter who captures Gray’s outward perfection on canvas and falls perilously in love with him.

To spice up the story and to make explicit Wilde’s generally vague allusions to the “sins” inherent in Dorian’s double life, the filmmakers insert some kinky but mostly heterosexual sex, including some brief scenes of bondage and masochism. Given Gray’s body’s miraculous ability to heal, the latter work rather well.

It is possible that the film may be attacked for cowardice because it does not make Gray mainly homosexual, but it is probably the right decision by the filmmakers. It makes it clear to a modern audience that what makes Gray a monster is not his particular sexual tastes, but his selfishness and ruthlessness in indulging every desire.

Nevertheless, for most of its length, and it feels rather longer than the 112-minute running time, Dorian Gray plays like a lavishly funded student film, albeit one made by plodding rather than brilliant students.

Even the CGI cityscapes of Victorian London look amateurish. That the film is watchable at all is down to Firth and the excellent Rebecca Hall (last seen in Woody Allen’s Vicky Cristina Barcelona), who plays Wooton’s suffragette daughter, a character invented by Finlay, and who seems to have wondered in from a different, more grown-up production.