A manhunt has been launched to locate six terror suspects who arrived in Britain on small boats, security sources say.
The illegal migrants – who all have links to Islamist groups – started their journey in Syria and travelled to Europe before crossing the Channel.
The radical group are said to be backed by Iran and plan to target the Government or public services.
Their arrival brings the total number of terrorist suspects who have used small boats to enter Britain this year to 25.
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It is thought that the group arrived from northern France weeks ago.
The movements of three of the fugitives are being monitored but the others, who are believed to be using fake identity documents, have vanished.
The decision to keep the known suspects under surveillance was made in a bid to locate the missing members.
However, any attempts to remove the group could lead to lengthy legal battles, anti-terror bosses have warned.
“The information indicates that these people are terrorists planning to attack government buildings in England, Scotland and Wales,” an intelligence source told the Express.
“Although they arrived without identification, we believe all are now in possession of false documents.
“They plan to commit an act which embarrasses the Government. This could mean damaging a building or even a close-proximity cyber attack, though we do not anticipate this is a mass-casualty event.”
Following the revelation, MPs have called on the Government to do more to stop small boats.
Following the revelation, MPs have called on the Government to do more to stop small boats
“This is yet another reason why firm action is needed,” Tory MP Marco Longhi told the Express.
“We already know the impact illegal migration has on housing, the NHS and local authority resources. This should provide a wake-up call about the threat to national security due to our vulnerable borders.
“It is terrifying to think we might not know the dangers posed by some of those already here.”
The plot was reportedly found by MI6 operatives stationed near Damascus before Hamas launched their ambush on Israel.