A Sydney-style terror attack could happen in Britain at any moment, Prime Minister David Cameron has admitted.
Asked by a committee of senior MPs how close the country was to a similar attack, Mr Cameron said: "The threat we face definitely includes those sort of self-starting sometimes quite random attacks that could happen at any moment in Britain.
"We've seen over the last few months there have been a series of plots that have been detected and prevented that would have seen police officer or other authority figures murdered in cold blood as Lee Rigby was murdered in cold blood.
"Its thanks to the brilliance of our policing and security services that these things have been prevented.
"But we can't count on them to prevent it every time.
Mr Cameron added: "People who are self-radicalised on the Internet who then suddenly do appalling things, that is much more difficult to prevent."
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"It was pretty loud, pretty frightening - like nothing I'd ever seen before ever," Greg Parker said.