Christian Bale and Heath Ledger star in the film
The BBFC has justified giving The Dark Knight a 12A certificate after getting more than 80 complaints about the Batman film's disturbing content.
The film regulator's spokeswoman Sue Clark said the sequel was a fantasy movie with only implied violence.
But she admitted that the British Board of Film Classification had carefully considered giving it a 15 rating.
The 12A rating states that a film should not "dwell on violence" and "does not emphasise injury or blood".
The film contains a scene in which The Joker, played by the late Heath Ledger, is beaten repeatedly by Batman in a police cell.
The BBFC ruled that the blows were "masked from the camera" and there was "no sign of injury".
The Dark Knight should be a 15 certificate
Keith Vaz MP, Home Affairs Select Committee chairman
It conceded that there was a "good deal of violence" in the movie, but said it adhered to the rules of the 12A certificate.
But Keith Vaz MP, who chairs the Home Affairs Select Committee, said the 12A certificate was too low, adding that he was concerned by The Joker's use of a knife in the film.
He told The Independent newspaper: "The BBFC should realise there are scenes of gratuitous violence in The Dark Knight to which I certainly would not take my 11-year-old daughter. It should be a 15 certificate."
Ms Clark emphasised the fantasy nature of The Dark Knight and its basis in comic books.
"Batman can jump off buildings and fly and The Joker is not a realistic character and bounces back with a smile on his face."
She added that a 15 certificate would have denied an important part of the superhero's fan base the chance to see the film.
"Younger teenagers would not have been able to see it, and they are the very people who are going to love it.
"We would have ended up with far more complaints from people who wanted to see the film and couldn't," said Ms Clark.
The Joker uses a knife as his signature weapon
She added that the number of complaints was low relative to the number of people who had seen the film.
Some 4.7 million tickets for The Dark Knight have been sold in the UK to date.
Box office success
Meanwhile, The Dark Knight is on track to become the second-biggest movie of all time after topping the North American box office for a third week.
The film took $43.8m (£22.2m), taking its total US haul to $394.9m (£200m).
Warner Bros said it expected the Batman film to take at least another $100m (£51m), surpassing Star Wars - the number two movie of all time in the US.
The sci-fi film took $461m (£234m). The current number one is 1997's Titanic, which took $601m (£305m).