It is a tender moment as the young black man hugs his girlfriend on the couch. But as the camera pulls away, you see the blood on her jumper where his hand has just been.

This is one of the poignant moments in a hard-hitting campaign launched by Scotland Yard to fight gun crime in the black community.

Police believe some people are too scared to report gangsters or do not want to "grass up" on friends.

The campaign highlights the guilt that will haunt people who do nothing about gun crime.

In a cinema advert, a group of young black men plays basketball. But the ball is soaked in blood when it falls through the hoop.

"If you know someone's got a gun and you don't report it, you could have blood on your hands," a voice warns at the end.

The launch coincides with the fifth anniversary of the Met's Operation Trident, a team of officers that deals with gun crime among black people.

Last year they investigated 162 shootings in the capital. In the 12 months up to March this year, 18 people were shot dead.

The cinema advert will be played across London, especially at theatres in areas worst affected by gun crime.

It was first shown today at the Ritzy cinema in Brixton, south London, with Met chief Sir Ian Blair in attendance.

The campaign also includes billboards with the message, "Stop the guns," and a radio advert with one victim's story.