Sean Bean's face looks so much like a big old craggy cliff that every year he has to fight off guillemots trying to nest in it.

Another fact about his face: the wrinkles form a perfect street map of his home town of Sheffield, which means that if you ever find yourself lost in that city, all you have to do is buy a DVD box set of Sharpe or Game Of Thrones and use the picture of Bean on the cover to find your way about.

His face is changing though, because Bean has been working in the US of late, which means he now has American teeth ie. white, bright and straight.

In his latest role as deep-cover FBI agent Martin Odum in Legends (Sky 1, Wednesday, 10pm), the teeth beam out of his face like a searchlight, which is hardly appropriate for an undercover operative. Wherever he is, you can spot him by the glare from his mouth.

His undercover job in the first episode was posing as a member of a group of Aryan supremacists.

We were told early on he had been undercover for about six months, which had screwed up his relationship with his ex-wife and his son.

This is par for the course: the leading men in police shows never have strong, stable relationships and it's the poor actresses who have to play the ex-wives I feel sorry for.

Their only job is to stand on the doorstep looking hacked off while the leading man picks up their kid for the weekend.

There is no doubt about Bean's credentials for this part though: mostly he plays growly, difficult tough guys and here he is again playing a growly, difficult tough guy, albeit one living undercover as a socially awkward, stuttery loner.

What is interesting is he appears to have been living with his false identity for so long that parts of it

are becoming real.

There was also interesting potential in the set-up which the drama failed to explore.

We all talk a lot about why Muslim men become radicalised and go to Syria and Iraq to train

as jihadists, but why do white men become radicalised and end up in extreme right groups?

Legends could have looked at that question, but didn't.

Instead, there was an awful lot of pseudo James Bond drama and it was also plagued by the curse of modern American drama, which is to chop the whole thing into ultra-short scenes.

Watching it was like looking at a picture through a picket fence.

But you know, Sean Bean has nice teeth. There is at least that.