Jihadis infiltrate House of Commons tour groups to plot terror raids on MPs: Cenotaph security crackdown as Canada killing sparks fears of outrage on Remembrance Day

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Islamic extremists have joined tour groups of Parliament to ‘scope out’ the building for a potential terrorist attack, intelligence sources have told The Mail on Sunday.

The disclosure, in the wake of last week’s gun attack on the Canadian Parliament, last night led to demands by MPs for Speaker John Bercow to restrict the number of visitors to the Commons.

One MP said it was a ‘wake-up call’ which proved plots to blow up Big Ben do ‘not just belong to the realms of Doctor Who’. An aide to Mr Bercow hit back, saying: ‘We must not hand a propaganda victory to the terrorists by shutting out the public.’

On guard: Security is being tightened for next month's Remembrance service, attended by the Queen

High alert: MPs have called for House of Commons tours to be restricted after the attack in Canada

This newspaper has learned security is also being tightened for next month’s Remembrance Day service, attended by the Queen and senior politicians, after fears were raised at the highest level about the public’s proximity to the dignitaries at the Cenotaph.

Up to three Islamic terror cells in the UK, thought to be plotting attacks on soldiers in the UK, have been tracked as they carried out surveillance on army barracks.

The UK is on a heightened state of alert after Muslim convert Michael Zehaf-Bibeau went on a rampage in central Ottawa, killing a soldier guarding the National War Memorial before storming the parliament building. The gunman was shot dead by the Canadian sergeant-at-arms, Kevin Vickers, as he headed towards the chamber in which MPs were barricaded.

After the attack, Prime Minister David Cameron spoke to MI5 boss Andrew Parker and Scotland Yard chief Sir Bernard Hogan-Howe about security at landmark buildings, including the Commons.

According to one intelligence briefing, individuals linked to terror groups have joined ‘history tours’ around Parliament.

Although visitors are banned from taking photographs inside the Palace, the tours allow them to study the layout of the building. More than a million members of the public enter the Palace of Westminster every year, and 3,500 closely vetted passholders work there.

The number is expected to rise as Mr Bercow has pledged to boost revenues by ‘selling’ access to business people, film crews and students.

Killer: Michael Zehaf-Bibeau was shot as he headed towards the chamber full of Canadian MPs in Ottawa

Last night Labour MP Barry Sheerman said: ‘What has happened in Canada is a wake-up call to us all. Opening up Parliament to tours is fine in principle, but it does carry big risks. The traffic through the Commons now is enormous.

‘When I raised this danger earlier this year I had my knuckles rapped. The former Commons Clerk Sir Robert Rogers accused me of being a scaremonger. But it does not just belong to the realms of Doctor Who for people to blow up Big Ben.’

However, one of Mr Bercow’s aides insisted the Commons would remain open to the public. ‘The Commons is much more secure than our Canadian counterpart, which was only on a medium level of alert,’ the aide said, speaking on condition of anonymity. ‘We have been at, or close to, the highest level of alert pretty much since the IRA threat in the 1970s. A gunman could not get anything like as close as that to our Chamber. We have procedures. And there are frequent exercises to deal with that scenario.

‘The day people would rather click on the internet to read about politics than come to Parliament to see it in action would be a dark day for democracy. We must not hand that propaganda victory to the terrorists.’

Four years ago foreign nationals were banned from tours of Big Ben after the uncovering of a plot to blow up the Stock Exchange, the US Embassy and the Houses of Parliament. In America, the White House has suspended access for foreign nationals wanting to take tours.

Fears have also been raised in Whitehall about Remembrance Day at the Cenotaph in a fortnight – honouring not just those from two World Wars but from the more divisive recent conflicts in Iraq and Afghanistan.

Security advisers are concerned the soldiers who flank the Royal Family and politicians stand backs to the public, which they worry is ‘too exposed’.