Terror attack on UK 'highly likely' as threat level raised

Police and security services have long been concerned over the large numbers of British jihadists travelling to Syria and Iraq.

It is feared more than 500 have gone and around half of those are now back in the UK, with some possibly planning attacks here.

At least one plot is known to have already been foiled.

The decision to raise the threat level, which is now only one stage below 'critical' - which means an attack is imminent - was taken by the Joint Terrorism Analysis Centre (JTAC).

Mrs May said: 'JTAC's judgements about that threat level are made on the basis of the very latest intelligence and are independent of Ministers.

'The increase in the threat level is related to developments in Syria and Iraq where terrorist groups are planning attacks against the West.

'Some of those plots are likely to involve foreign fighters who have travelled there from the UK and Europe to take part in those conflicts.

^{Home Secretary Theresa May}

'The first and most important duty of government is the protection of the British people. We have already taken steps to improve our powers and increase our capabilities for dealing with the developing terrorist threats we face.

'That process will continue and the British public should be in no doubt that we will take the strongest possible action to protect our national security.

National threat levels

There are five levels of threat used by the JTAC:

* Critical - an attack is expected imminently

* Severe - an attack is highly likely

* Substantial - an attack is a strong possibility

* Moderate - an attack is possible but not likely

* Low - an attack is unlikely

'We face a real and serious threat in the UK from international terrorism. I would urge the public to remain vigilant and to report any suspicious activity to the police.'

Assistant Metropolitan Police Commissioner Mark Rowley, National Policing Lead for Counter-Terrorism, said: 'The threat level from international terrorism has changed from SUBSTANTIAL to SEVERE in response to the developments in Syria and Iraq.

'This means it is highly likely that a terrorist attack could happen in the UK.

'We therefore continue to urge the public to remain vigilant and to report any suspicious activity to police. We need communities and families to bring to our attention anyone they perceive may be vulnerable, a danger or escalating towards terrorism.

'From this afternoon we will begin to increase our levels of visible patrols and implement other security and protection measures. We will also build on existing community relations to provide reassurance and seek their support and assistance in keeping the UK safe.'

Anyone with information is urged to contact the Anti-Terrorist Hotline on 0800 789 321.