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."
Prime Minister David Cameron has paid tribute to the hostages "murdered" in the siege in Sydney, Australia.
Speaking before the Liaison Committee, Mr Cameron said: "In Australia there are tales of extraordinary bravery and sacrifice that are now being told about what happened in that cafe.
"I think that's what we'd expect from the people of that remarkable and great country and our thoughts are with them".
The family of mother-of-three Katrina Dawson who died in a siege at a Sydney cafe have said they are devastated by her "tragic and senseless death".
"We are shocked and devastated by the tragic and senseless death of our darling Katrina," a statement said.
"She was an amazing woman and the most loving and loved wife, mother, daughter, sister, aunt, in-law and blessed with a wonderful circle of friends and colleagues.
"We would like to thank everyone who has provided their support and wishes over the past 48 hours and ask that we be allowed to support each other in private."
The siege at a cafe in Sydney will change Australia forever, a journalist has predicted.
Mike Bowers, the picture editor for the Guardian Australia, who was at the scene in Market Place when the deadly siege came to an end, said Australians had been left "deeply shocked" by the incident.
"There is no doubt these things change a country," Mr Bowers told ITV News.
The dramatic moment armed police brought the Sydney siege to a bloody end has been caught on camera.Read the full story ›
"It was pretty loud, pretty frightening - like nothing I'd ever seen before ever," Greg Parker said.Read the full story ›
Tributes have been paid to two hostages who were killed in the Sydney cafe siege.Read the full story ›
Police numbers have been increased across Sydney in response to yesterday's cafe siege which left two people dead, senior New South Wales officers have said.
There will be an increased police presence in public places, transport hubs and iconic locations such as the city's harbour.
Mick Fuller, the force's assistant commissioner, said the aim was to ensure all residents felt safe "during these testing times".
“We want the community of Sydney and for that matter NSW, to go about their day to day business with confidence and comfort in the knowledge they are safe,” assistant commissioner Mick Fuller said.
The New South Wales Police commissioner said he "couldn't be sadder" following the deaths of two hostages in the Sydney cafe siege.
Andrew Scipione told reporters: "It's incredibly sad - I don't think I could be sadder."
A Sydney DJ who spoke to one of the hostages trapped in the Lindt Chocolate Cafe has recalled the demands made by the lone gunman.
Ray Hadley told Good Morning Britain one of the hostages called 2GB radio station where Mr Hadley works, and relayed demands made by Man Haron Monis.
"He wanted an ISIL flag - pretty simple requests - he wanted to speak to the Prime Minister for five minutes. And he wanted the government...to say it was an ISIL terrorist plot and he wanted that broadcast on the radio."