Fans of both FC Zurich and rivals Grasshoppers agreed to enter the Letzigrund Stadium ten minutes after the start of the match to show their anger at plans to clamp down on trouble that has plagued recent matches.

However, viewers tuning in to Swiss broadcaster SRF’s coverage of the match were baffled to hear crowds chanting when images showed a near empty stadium.

Now television chiefs have apologised for adding the bogus crowd noise.

A spokesman said: ‘In order to make the report as attractive as possible, the chants of the fans were subsequently edited into highlights of the game.

‘The decision was taken under great time pressure. It was wrong and we apologise for it. Manipulation of sounds or images is not allowed.’