Britain could be hit 'at any moment' by a Sydney-style terror attack, David Cameron told MPs last night.

The Prime Minister said the Australian attack, in which two hostages died and Islamic extremist Man Haron Monis was killed, was a reminder of the danger Britain faces.

He said it was only through the efforts of the security services that plots to murder UK police officers ‘in cold blood’ had been foiled in recent months.

Prime Minister David Cameron said Australia was a country 'very close to our hearts', and warned the attack in Sydney could be repeated in the UK

Mr Cameron told MPs on the Liaison Committee that the threat Britain faced 'definitely' included lone-wolf attacks like in Sydney

But he warned it was much harder for the authorities to prevent attacks by fanatics who are ‘self-radicalised on the internet’ than to tackle known extremists who had travelled to the Middle East.

The Prime Minister, appearing before senior MPs at the Commons Liaison Committee, 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 officers or other authorities murdered in cold blood.

‘It’s thanks to the brilliance of our security services that these things have been prevented.’

But he added: ‘We can’t count on them to prevent it every time because it is one thing understanding the terror networks coming out of Pakistan or Afghanistan or Iraq and Syria, trying to monitor what they’re doing, who’s going and who’s returning. That’s one thing.

‘But people who are self-radicalised on the internet, who then suddenly do appalling things, that is much more difficult to prevent.’

The Prime Minister's remarks come amid widespread horror at the twin terror attacks in Sydney and Pakistan which have left more than hundred people dead.

In Sydney, the Iranian asylum seeker Monis struck terror into the heart of the city's financial district after taking 17 staff and customers hostages inside the Lindt cafe in Martin Place for 16 hours.

The 50-year-old gunman is believed to have fired the first shots, which sparked teams of heavily armed police to swoop on the café at 2am on Tuesday.

Tori Johnson, the café manager, and barrister mother-of-three Katrina Dawson were the two hostages killed during the bloody climax to the stand-off.

The tragedy came before Taliban gunmen stormed a school in Pakistan and slaughtered 132 children today.

The 34-year-old manager of the Lindt cafe, Tori Johnson (left), and mother of three Katrina Dawson, 38 (right), have been named as the two hostages killed during the Sydney siege on Tuesday morning

FEARS MILITARY HARDWARE FROM AFGHANISTAN COULD BE ATTACKED BY TERRORISTS Convoys of UK and American military hardware being shipped back from Afghanistan could face attack by terrorists, it is feared. Thousands of vehicles and containers of equipment are being brought home as part of the withdrawal of Nato combat troops. Some will be transported by land and sea, via Pakistan. But one of the main routes to the port of Karachi is through Peshawar, the scene of yesterday’s Taliban attack. A second, more southerly route goes via the city of Quetta, a base for the Afghan Taliban that has been plagued by sectarian violence. Advertisement

Speaking before the siege in Australia came to an end yesterday Mr Cameron warned that the tragedy may have been played out more than 10,000 miles away, but it could be repeated in Britain.

The security services have warned ministers that an attack in the UK from such a fanatic is ‘almost inevitable’.

Andrew Parker, the director of MI5, warned last year that Britain was facing a grave terror threat, including from ‘several thousand’ Islamist extremists who are living here and want to attack the country.

In August, the UK’s threat level was raised from ‘substantial’ to ‘severe’ amid increasing concerns that hundreds of jihadis were returning to British streets from the wars in Iraq and Syria.

Last week, police forces across Britain were put on alert after a warning of an Islamist plot to kidnap and behead an officer.

More than 7,000 officers in the West Midlands – the UK’s second-largest force – were warned they were in imminent danger following a telephone threat.

It follows last year’s savage murder of soldier Lee Rigby in broad daylight. There are also fears that hundreds of people are being radicalised in British prisons.

The soldier was murdered by two Muslim converts who ambushed him as he walked back to his barracks in Woolwich, South East London, last year.

Mr Cameron called on Muslim communities in Britain to do more to stand up, oppose extremists and say they are ‘not speaking in my name’.

He suggested the perception of Muslims as ‘victims’ must be challenged as part of efforts to stamp out radicalism.

Gunman Man Haron Monis, pictured here protesting charges against him earlier this year, held 17 people hostage in the Lindt cafe

He admitted it was a ‘worry’ so many people seemed to be being radicalised in public institutions such as schools.

But he said the Coalition’s proposed new duty on figures of authority to report concerns about radicalisation could help to address the problem.

The Prime Minister told LBC Radio: 'Obviously it's an extremely worrying situation. It demonstrates the challenge we face of Islamist extremist violence all over the world.

Met police chief Sir Bernard Hogan-Howe warned of the threat posed by lone wolf attacks

'This is on the other side of the world but is the sort of thing that could just as well happen here in the UK or in Europe.'

He said Australia was a country 'very close to our hearts', adding: 'We very much stand with the Australians at their time of need. It is a reminder of the threat that we face and the need to be vigilant.'

Police and security officials have warned it is 'almost inevitable' that Britain will be hit by an attack by fanatics who have been 'militarised' by Islamic State.

Mr Cameron announced last month that an extra £130million will be made available over the next two years for the security services to 'monitor and disrupt those self-starting terrorists'.

A new legal obligation will be imposed on universities, prisons, councils and schools to play their part in tackling 'this poisonous extremism', the Prime Minister said.

Mr Cameron told MPs: 'The reason for providing some extra money today is that there is a specific and growing challenge from these self-starting—they are sometimes called 'lone wolf'—jihadis, who have been radicalised on the internet because of what has been happening in Syria but are not necessarily linked up with other terrorist networks.

'That puts extra pressure on and we need to respond to that.'

The security agencies face unprecedented pressure to prevent similar attacks by extremists acting alone, but it is much harder to detect and disrupt plots if they are not part of a wider terror network.

Met police chief Sir Bernard Hogan-Howe warned: 'It doesn't take an awful lot of organising, doesn't take too many to conspire together, there's no great complexity to it.

'So that means we have got a very short time to interdict, to actually intervene and make sure that these people don't get away with it.'

Unveiling new laws to counter the extremist threat, Home Secretary Theresa May revealed 40 terrorists plots have been thwarted in Britain since the July 7 attacks nine years ago.

The foiled atrocities including 'marauding' 'Mumbai-style' gun attacks streets, an attempt to blow up the London Stock Exchange and airplanes, and murder troops and a British ambassador.