Security wristbands enforced on Spears' TV set

The cast and crew of 'How I Met Your Mother' have been forced to wear wristbands on the US sitcom's set while Britney Spears is filming her cameo role - to prevent passers-by from snapping the singer at the studio.

The show's star Neil Patrick Harris was mistakenly refused entry to the stage - because he wasn't wearing one of the exclusive bands security officials issued to keep civilians out.