The three water cannon bought by Boris Johnson are costing more than £25,000 a year to insure and maintain – despite never being fired.
The London mayor snapped up the three second-hand Wasserwerfer 9000 riot trucks from the German federal police in 2014 for £218,000.
But the water cannon – which cost £23,573 to re-paint in the colours of the Metropolitan Police – are not allowed to be used on Britain’s streets.