British police will now have new powers to seize passports of terror suspects and stop extremists from returning to the UK, Cameron told MPs in his statement to the House of Commons.

"We will introduce specific and targeted legislation...providing the police with a temporary power to seize a passport at the border during which time they will be able to investigate the individual concerned," he said.

"Adhering to British values is not an option or a choice. It is a duty for all those who live in these islands so we will stand up for our values, we will in the end defeat this extremism and we will secure our way of life for generations to come," he added.

Describing as ‘abhorrent’ the fact that British citizens had ‘declared their allegiance’ to groups like Islamic State (IS), he said the UK was also looking to bar suspects from returning the UK.

The statement to MPs comes after the UK's terror threat level was raised to ‘severe’ from ‘substantial’ on Friday.

Among the new measures announced include legislation to be drawn up to give the police new statutory powers to confiscate the passports of suspected terrorists at UK borders; the UK will challenge any attempt by the courts to water down these powers; plans to block suspected British terrorists from returning to the UK will be drawn up on a ‘cross-party basis’.

The new powers also include Terrorism Prevention And Investigation Measures (TPIMS) to be extended, to include the power to relocate suspects; and airlines will be forced to hand over more information about passengers travelling to and from conflict zones.

Cameron said the UK was able to block foreign nationals and those with dual citizenship from re-entering the UK but did not have the same power for UK nationals deemed to pose a threat to the country.

Under his proposals, UK nationals suspected of being involved in terror acts would be allowed to keep their British citizenship, but they would be prevented from re-entering the UK for a period of time.

According to some estimates, 500 British jihadists are believed to be fighting in the two countries, both of which are facing a major offensive from the Islamic State (IS) militant group.

Fears about British fighters joining jihadists were fuelled last month by a video showing the killing of US journalist James Foley by IS, which featured a man with a London accent.

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