Islamic State may be planning "enormous and spectacular" attacks against the UK, the national head of counter-terrorism policing has warned.
Assistant Commissioner Mark Rowley said the threat from the group which has taken over large parts of Syria and Iraq was evolving, and that it was keen to repeat incidents such as last year's Paris shootings and suicide attacks that killed 130 people.
"What we are now seeing in recent months ... is the broadening of that threat, more plans to attack Western lifestyle ... going from that narrow focus on police and military and symbols of the state to something much broader," said Rowley.
"You see a terrorist group that has big ambitions for enormous and spectacular attacks, not just the types that we've seen foiled to date." This, said Rowley, was the "natural next step" for the group.
British security chiefs have previously warned the biggest threat posed by the group was the radicalisation of young Britons over the internet and the danger posed by those who joined the fighting in Syria and Iraq to return home to carry out attacks.
About 800 British citizens are thought to have travelled to Syria, many to join IS, since the outbreak of civil war.
Rowley said recent arrests showed that IS was adopting a different methodology in trying to get fighters into northern Europe who had weapons and paramilitary training.
"Terrorist groups have always wanted to do the grand and the more spectacular attack because it gets more impact," he said.
He said British police had made more counter-terrorism arrests in 2015 than in any previous year including a marked number of women and people aged under 20.
Britain's terror threat rating is currently rated "severe", one level below "imminent".
Last year the Metropolitan Police carried out a major "stress-test" exercise in London to see how the capital would respond to a Paris-style attack. The results have been kept secret but many of London's buildings are now surrounded with bollards designed to resist bombs.
Additional reporting by Reuters.
