Spies to vet airline flight lists for returning jihadis as Saudi king warns: 'Terrorists could attack Europe within a month'

• Airlines would be forced to handover more information about passengers
• Flights containing travellers on 'watchlists' may be prevented from landing
  
• Comes as king of Saudi Arabia warns terror strikes could be imminent
• David Cameron set to unveil range of new security measures today
• He wants to ban extremists from returning to UK after fighting abroad

The Prime Minister is to give intelligence agencies the power to vet airline flight lists in an effort to stop jihadis entering Britain.

The US-style laws would compel all airlines flying into the country to provide much more information about passengers.

If the name of a traveller appears on a ‘watchlist’ the plane may not be permitted to land in the UK unless the person is stopped from boarding .

The Government wants to improve the flow of airline passenger data to intelligence agencies. At present, some airlines do not release their passenger lists until 30 minutes before flights leave.

There will also be a push to share more data on passengers, but this will run into difficulties in the European parliament on civil liberties grounds.

The airline flight lists measure is among a number of emergency powers which will today be unveiled by David Cameron.

It follows a warning by the king of Saudi Arabia that terror groups could attack in the West within a month.

He said: ‘If neglected I’m sure they [terrorists] will reach Europe in a month and America in another month. The evils of

terrorism must be fought with force, reason and speed.’

At the centrepiece of Mr Cameron’s plans will be a temporary ban on British citizens from coming home if they have travelled to fight alongside Islamist fanatics.

This would stop short of stripping suspects of their British citizenship and making them stateless – a breach of international law – but at the same time prevent them from re-entering.

Under existing laws, the Government has the power to block only foreign nationals, those with dual citizenship or naturalised citizens.

Mr Cameron and Deputy Prime Minister Nick Clegg were last night thrashing out the final details ahead of a statement in the Commons this afternoon.

They acted after intelligence chiefs raised the UK’s terror threat level to ‘severe’ – the second highest level – after warnings that a jihadi atrocity was ‘highly likely’.

A temporary ban is likely to require major changes to air transport legislation.

A Downing Street source said: ‘We need to make sure this is legally robust. It is a difficult thing to achieve, putting a temporary ban on people without making them stateless, but it is vital we achieve it.’

Ministers are also considering strengthening Terrorism Prevention and Investigation Measures – so-called Tpims – which replaced control orders.

The Government is also expected to make it easier to seize the passports of potential terrorists to

prevent them travelling to trouble-zones.

So far, 23 potential jihadis have been barred from leaving. Under the plans, border guards would be allowed to revoke a fanatic’s passport.

Defence Secretary Michael Fallon said new measures were needed to deal with ‘gaps in our current armoury’ against terrorism.

At least 500 people from the UK are thought to have gone to fight in Syria, but the number could be as high as 2,000. Security chiefs believe some 250 have already returned home and may have been brainwashed into launching strikes here.

Up to 20 Britons are believed by Turkish authorities to be waiting in safe houses for instructions to cross into Syria.

Intelligence and anti-terror specialists are also examining entry records of all Britons to Turkey, cross-checking those who have left, how long they stayed and those who have overstayed the 90-day visa period.

Some are said to be using the passports of fellow fighters of similar age and appearance to avoid detection