British actor Benedict Cumberbatch has spoken out to defend his detective show Sherlock over a controversial new storyline about a terrorist attack on the London Underground.

The Star Trek Into Darkness actor will reprise his role as Sherlock Holmes when the series returns for a third season in the New Year (14), and the first episode will show the super-sleuth battling to prevent an explosion on the British capital's Tube train network.

The plot has sparked comparisons to the real life attacks on the Underground system in 2005, when suicide bombers killed 52 commuters and injured more than 700 by detonating explosions on the city's Tube and bus networks, but Cumberbatch is adamant the story has been treated sensitively.

He tells Britain's Daily Mirror, "We have had terrorism in our Underground. It (the storyline) was not treated lightly."

The show's creator Steven Moffat insists the story is "tasteful".