Boris Johnson is the Mayor, not the Lord Mayor (which is a very different office), but, no, he didn't.
And I'm honestly not sure it could be stopped now in similar circumstances.
But since the riots of 2011, the structure of supervision over the Metropolitan Police has been quite dramatically changed partly because of what happened in 2011 - the Metropolitan Police Authority (which as well as the Mayor, also involved about half of the elected London Assembly - a clear case of 'too many chiefs') was abolished and replaced with the Mayor's Office for Policing and Crime, which gives the Mayor personal and direct influence over the police. He can react faster and give orders faster in an emergency. Whether it will work remains to be seen, but it does look like a greatly improved and much more efficient command structure - the Mayor can deal directly and personally with senior Police, including the Commissioner and Deputy Commissioner, with the members of the London Assembly only being able to review decisions after the fact - holding him accountable for errors, but not blocking decisions at the time.
Thank you for the Lord mayor correction.
It’s a nice thing to see they’ve revamped the chain of command, but given the destruction of the last riots, do they really want to road-test it?