He said: “In recent months we’ve seen a broadening of that, much more plans to attack Western lifestyle, and obviously the Paris attacks in November.
“Going from that narrow focus on police and military as symbols of the state to something much broader. And you see a terrorist group which has big ambitions for enormous and spectacular attacks, not just the types that we’ve seen foiled to date.”
He added: “You see a terrorist group that whilst on the one hand has been acting as a cult to use propaganda to radicalize people to act in their name … you also see them trying to build bigger attacks.”
Mr Rowley, who is the national policinglead for counter-terrorism, said that IS is trying to get supporters who have received military training in Syria into northern Europe to stage attacks.
Mr Rowley said the “shared effort to look for any possible links of those networks or other networks that have reached the UK is obviously a massively high priority”.
In the last three years the number of arrests of terrorist suspects has risen by 57% compared to the previous three years.
Around half lead to a charge. Last year just over three-quarters (77%) of those arrested were British nationals, 14% were female and 13% were aged 20 and under.
The number of girls and women and the number of teenagers is a new trend, Mr Rowley said.
“That would not have been the picture that one would have seen a few years ago. That is an indication of that radicalization, the effect of the propaganda and the way the messages of Daesh (IS) are resonating with some individuals,” he added.
Scotland Yard has seen more than 20 families and around 50 young people go through family court proceedings over concerns about radicalization in the past year.
Police are beginning to use trained psychologists who can provide advice both about how to deal with those at risk of being influenced by extremists, as well as terrorists in the event of an attack.
The number of trained firearms officers across the UK is also being increased in the wake of the Paris atrocities, which saw 129 people killed in co-ordinated attacks by extremists.
Official advice was issued at the end of last year to “Run, Hide, Tell” if marauding gunmen are found to be on the loose – meaning get as far away as possible, hide, and if possible call the police.