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10 July 2014, 11:19 | Updated: 10 July 2014, 11:23
Boris Johnson has confirmed that water cannon have been shipped to the UK and are being prepared for use in London despite police not yet having official permission to deploy them.
Speaking to the Police and Crime Committee at City Hall the Mayor said the cannon are being tested at a secret location.
He said: "They are being prepared for use in this country and obviously we await the certificate from the Home Office."
Home Secretary Theresa May has to grant permission for them to be used on the UK mainland; they have been available in Northern Ireland for several years.
When asked whether they will be used in London this summer, Mr Johnson said: "I would oppose the use of water cannon except in the most exceptional circumstances.
"There are very few circumstances in which I would wish to see water cannon deployed at all.
"This novel use of crowd control should be properly tested. I have said very clearly and publicly that I will be happy to have a go myself."
Metropolitan Police commissioner Sir Bernard Hogan-Howe told the committee that the work on the three cannon, bought from Germany, includes making sure they have cameras fitted to allow evidence gathering.
He said: "We think it will be rarely used and rarely seen. We don't expect to see it deployed hardly at all."