The man who led the investigation into the 7/7 bombings has warned that the terrorist threat to the UK is as great as it has ever been.
Peter Clarke, who was head of Scotland Yard's Counter Terror Command at the time of the London attacks, said the authorities were now "working incredibly hard" and were "stretched to the limit" as they tried to counter the terrorist threat.
In an interview marking the 10th anniversary of the bombings, the now retired Deputy Assistant Commissioner told Sky News: "We've seen some awful attacks in this country such as the murder of Lee Rigby and there doesn't seem to be any slackening in pace of the numbers of young people being attracted to extremism.
"You only have to look at the hundreds of people who it's believed have now travelled to Syria to take part in the conflict there."
Mr Clarke said in addition to Syria and Iraq, there were now also British citizens involved in conflicts in many parts of the world.
Ten years on from the London Tube and bus attacks, the threat has evolved: large-scale, al Qaeda-inspired bomb plots have given way to less sophisticated threats.
Those plots, which include planned knife and gun attacks, are just as terrifying to the public and are more frequent.
Terror-related arrests in the UK are at their highest ever level , running at one arrest every day or two.
Many of those arrests relate to young Muslim men and some women, who are planning to travel to Syria to fight alongside groups like the so-called Islamic State.
Raffaello Pantucci, Director of International Security Studies at the Royal United Services Institute, said some of those who were currently fighting alongside IS would eventually pose a threat to the UK.
He said Syria and Iraq were just the latest examples of conflict zones where jihadists become battle hardened before many eventually return home.
"In all these places, once you've had this sort of radicalised community that is keen and mobile to go out and participate in the fighting, some of those people will come back and show up in terrorist plots here.
"It's happened in every single terrorist struggle so far. It's already happening when we're looking at Syria and Iraq."
Scotland Yard's current head of counter terrorism policing has warned that many young Muslims are also being radicalised and sent down a path towards violent extremism without even leaving the country.
Metropolitan Police Assistant Commissioner Mark Rowley appealed to communities to "step forward" in the fight against radicalisation, saying their help was now more crucial than ever to security services' efforts to prevent fresh attacks.
Mr Rowley said officers are now faced with a "completely different profile" as IS exploits modern technology in an attempt to create a "violent cult".
"We are not simply confronting a terrorist organisation like al Qaeda or like the IRA which works in a secret way and plots and plans what it wants to do secretly.
"We are dealing with an organisation that uses marketing, uses the internet and is trying to create a corrupt violent cult that is going to act in its name."
Mr Clarke said that, although police and the security services were working hard to disrupt potential plots, he was concerned efforts to counter the extremism narrative were less successful.
"I'm afraid I'm rather pessimistic 10 years on about where we've moved to in terms of promulgating the message that violence doesn't achieve anything and is not the answer to anything. What we are seeing is still intolerance.
"Stopping people being drawn into violent extremism is a difficult balance and I'm not sure that we've yet got it right."
Meanwhile, the head of MI5 has warned of a "serious societal and security challenge" ten years after the bombings.
"In the preceding months, there had been a degree of scepticism about the terrorism threat in the media: surely it couldn't happen here? The fact of 7/7 ended those arguments and led to a step-change in the nation's counter terrorism defences," Andrew Parker said.