Cameron in Seoul on the London student protests
"I was worried for the safety of the people in the building because I know people who work in there - not just in the Conservative Party but in other offices as well," the prime minister told me this morning.
Last night, on arriving at his hotel in the South Korean capital Seoul, David Cameron and his aides watched live coverage on BBC World News of a peaceful student protest turning into a violent assault on his party's HQ. Wry amusement that they had missed the protests soon turned into alarm when they heard that protesters had not just smashed through police lines but had also made it up several storeys to within feet of the staff working there. They were only turned back by a quick-thinking security guard who pretended that they'd got the wrong floor.
The prime minister told me:
"What I felt when I saw those pictures was: Of course people have a right to protest peacefully, but I saw people who were bent on violence and on destroying property and that is completely unacceptable. We need to make sure that behaviour does not go unpunished."
He praised the "extremely brave" police officers manning what he called "the thin blue line" which could not prevent protesters breaking through and insisted that it must not happen again.
"They were very brave, those police officers; but as the police themselves have said, there weren't enough of them and the police response needs to reflect that. So I'm very glad that the Metropolitan Police Commissioner has said what he's said and I think we need to learn the lessons very rapidly."
I put it to the PM that we could be seeing a re-run of the Thatcher years. He denied that, claiming that the fact that this government is a coalition ensures that this is not a case of back to the future.
On this, the morning after the riot before, David Cameron has had to turn his attention elsewhere. He has already marked Remembrance Day with veterans of the Korean War, met FIFA's vice-president to sell England's World Cup bid and now has the small matter of the G20 summit of world leaders to attend to.
On his mind, no doubt, is the question: "Is this what it will be like from now on?"