Makers of a high-tech police anti-riot vehicle are facing some tough questions after the £820m vehicle was badly damaged by eggs and tennis balls.

Germany has ordered 78 of the WaWe 10 water cannon-equipped vehicles which Austrian manufacturer Rosenbauer boasts can handle the toughest situations.

The problems came to light when police chiefs in the central province of Thuringen, decided to stage a display to show off their newest acquisition.

Police officers threw eggs, tennis balls and plastic bottles filled with water at the vheicle to simulate rioters armed with bricks, stones and petrol bombs.

Unfortunately the 'harmless' ammunition left huge dents in the armoured glass of the 33 tonne vehicle.

The scandal came to light when the police were forced to ask the Interior Ministry for the money to repair the damage.

The Interior Ministry is now demanding an explanation from Rosenbauer as to how the 'riot-proof' vehicle could be so easily damaged.

A police spokesman said that the vehicle could still be used but they were now waiting for an expert to decide whether the glass needed to be replaced.