An Islamist holds aloft the Isis flag at a demonstration in Tunis. (Getty)
An Islamist holds aloft the Isis flag at a demonstration in Tunis. (Getty)Getty

Britain's Home Secretary will ban insurers from paying ransom demands by terrorist groups such as the Islamic State (Isis), after a surge in hostage seizures over recent months.

Theresa May is set to announce the additions to the Counter Terrorism and Security Bill later on today [24 November] in order to tackle rising instances of groups using hostages and ransoms to fund their operations.

"So far this year, we have disrupted several attack plots and made 271 arrests," said Metropolitan Police Assistant Commissioner Mark Rowley, who is leading the country's national counter-terrorism policing campaign.

"They are no longer a problem solely stemming from countries like Iraq and Afghanistan, far away in the minds of the public.

"Now, they are home grown, in our communities, radicalised by images and messages they read on social media and prepared to kill for their cause.

"We don't want to scare people but we do want them to understand the threat and be vigilant to things that are out of place or suspicious and report it to the police."

Britain's terror threat level was heightened to "severe", from "substantial", because of rising conflicts in Iraq and Syria.

Following May's announcement, UK counter-terrorism police are set to brief more than 6,000 people at a range of places, such as airports, shopping centres, and even farms, on being more vigilant over potential threats.