The Scotland Yard boss said public order officers did identify some buildings that could be vulnerable to demonstrators but not the Millbank Tower complex.
He said an internal review of what went wrong on November 10 boiled down to the fact many more people turned up than police expected.
And he said officers were caught out after a long period of peaceful student demonstrations and their good relationship with organisers.
Speaking at City Hall, Sir Paul said he received the results of the “quick time” review, undertaken by Commander Simon Pountain last night.
He said: “The bottom line for me is far more demonstrators turned up than we expected. We did not have any intelligence that there would be significant disorder or violent conduct.
“We had identified a number of vulnerable premises but regrettably we did not identify some of the right premises.
“We have to be honest about that and we did not identify the party headquarters that was invaded.
“Public order is not an exact science and the people who do it overwhelmingly get it right.”
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