Five years after John le Carre's novel Tinker Tailor Soldier Spy was published, the BBC adapted it for television in 1979, with a seven-part series starring Alec Guinness as the elderly agent George Smiley. It not only soon became part of the Beeb's canon of classic TV, but it even spawned a sequel Smiley's People, with Sir Alec reprising his role.

Somewhat surprisingly, considering the current appetite that exists for remaking existing films and TV shows, it's only now that the powers that be have decided to dust down old Smiley and his suspicious pals for a big screen outing. At the helm is Swedish director Tomas Alfredson, who is making his first English language film after the success of his debut feature Let the Right One In.

Despite serving his country well for a number of years within British intelligence, it's been decided that George Smiley (Gary Oldman)has reached that point in his career where he should retire, whether he likes it or not.

His forced retirement is soon seen as somewhat premature however, when it comes to the attention of the Circus (the code name for MI6) that there is a mole working in cahoots with the Russians within their ranks, and Smiley is the best man to sniff him out.

With the help of young agent Peter Guillam (Benedict Cumberbatch), Smiley begins to examine the pieces of a complex puzzle in order to discover who the MI6 mole really is.

And here's your starter for ten - name the quiz show for university students. Anyone?

The film's premise may well be a relatively simple one, but the screenplay does its utmost to keep audiences on their proverbial toes. The story is rich with characters, so much so that it unfolds not so much as a whodunit but, more accurately, as a whoisit.

This allows many of the cast to go to town in fleshing out their respective characters, almost to the point of caricatures. Everyone except Oldman however, who plays Smiley with the greatest of restraint. It would be an impressive performance if it didn't feel so much like an impersonation of Guinness; so much so that you half expect Oldman to utter the words "these aren't the droids you're looking for". Sir Guinness would surely be flattered, but it's somewhat of a wasted opportunity on Oldman's part, who had the chance to create his own version of this curious character.

Elsewhere though, Cumberbatch in particular gives a great account of himself, as do Colin Firth, Toby Jones, Mark Strong, John Hurt and Tom Hardy, who almost makes amends for his participation in the dreadful Warrior.

Perhaps part of this failure to reinvent Smiley is down to Alfredson; at times it appears that his priority was in making the film feel authentically set in the seventies, which he does so with remarkable accuracy and aplomb. Alfredson has created a cinematic sponge which he's dipped into that particular decade and soaked up every bit of it. In that respect, it's a massive achievement.

Where the Swede may have taken his eye off the ball however, is in the last third of the film, which appears to unravel itself into a disappointingly anti-climatic ending. After making the audience work so hard for the majority of the film, the pay-off is lukewarm in comparison.

There's no doubt that Afredson had a great vision for the film, but his execution of the latter stages of it, allows this version of le Carre's story to fall short from being the instant classic it came so close to being.