Thousands of pounds has been spent maintaining three water cannon in Kent for the UK’s largest police force, despite them never being used.

Former Mayor of London Boris Johnson authorised the purchase of the second-hand trucks from Germany for the Metropolitan Police two years ago as a response to the London riots of 2011, at a cost of more than £200,000.

Since then they have been kept at a police training facility in Gravesend after they were banned by then-Home Secretary Theresa May, but more than £25,000 has still been spent ensuring they are kept in good condition and insured.

A Freedom of Information request submitted by our sister paper - the Gravesend Messenger - found that each cannon has cost £6,960 a year to maintain and £1,606 to insure — a total of £25,618.

Mr Johnson’s successor Sadiq Khan said last month that he would be selling the cannon and that all money raised would be used to fund youth services.

Speaking during his first State of London debate on June 30, as reported by the Evening Standard, Mr Khan said: “I am going to sell them and use the money for youth services.

“This shows the inability of Boris Johnson to get a good deal. These were second hand and he paid almost £250,000. We are paying for storage facilities for these water cannon and that beggars belief.”

Mrs May also teased Mr Johnson over his deal for the cannon when she announced her intention to run for leadership of the Conservatives.

She said: “I seem to remember last time Boris did a deal with the Germans he came back with three nearly-new water cannon.”

Mrs May appointed Mr Johnson as her Foreign Secretary when she was officially sworn in as Prime Minister earlier this month.