German police sue after beating

The officers' special password was of little use

German police officers have mistakenly beaten up two of their own undercover detectives, leaving the authorities facing an embarrassing lawsuit.

The incident happened on Saturday 16 November in Hamburg, when police officers were monitoring a rally of some 3,000 people protesting against the demolition of illegal squatters' homes.

Two plain-clothes agents infiltrated the crowd to send information to their colleagues.

But late in the evening violence broke out and several hundred helmet-clad riot police clashed with the protesters - including the undercover detectives.

A spokesman for the two plain-clothes agents said that even though they had given their fellow officers a secret password, they were still beaten up.

Both officers suffered head injuries from the incident and they are now taking legal action.

The local police union described the incident as regrettable, and said it was in no way "evidence of more widespread aggression within the police force".