The threat of terrorists crossing by ferry from Northern Ireland to Scotland is real and substantiated, the former terrorism reviewer has warned.
Officers at the Scottish ports of Loch Ryan and Cairnryan said passenger information from ferry companies was “incomplete and unreliable”.
Since 2014 the terror threat in Scotland has been “severe”, with an attack highly likely.
Reviewer David Anderson QC wrote: "The threat of terrorists crossing from Northern Ireland to Scotland is a real and substantiated one.
"The Canary Wharf truck bomb of 1996, manufactured by the IRA in South Armagh, killed two people, injured more than 100 and caused £150 million (€171 million) worth of damage.
"It was transported from Larne to Stranraer on a Stena Lines ferry, then driven to London."
That attack was more than 20 years ago, before the 1998 Good Friday Agreement which cemented the peace process.
Police Scotland this month launched a campaign urging the public to help defeat terrorism.
The terrorism reviewer’s report was published before he left office at the start of March.
He said passenger lists for ferries connecting Belfast and Larne in Co Antrim to the Scottish west coast were incomplete and unreliable, warning port security had been impaired by shortcomings.
“On my visits in 2015/16 to the seaports of Kent and to Cairnryan and Loch Ryan in the south-west of Scotland, the common and strongly expressed refrain from ports officers on the ground was that they could do their jobs more effectively if they had better advance information about passengers arriving (and departing) by sea.
“In the absence of such information, it is impossible to target stops as precisely as it is, for example, at airports where advance passenger information is widely available.”
He endorsed the view of officers at Irish Sea ports that better quality information, provided reliably and in advance, would substantially improve their ability to target examinations of passengers effectively.
A statement from Police Scotland said: “While there is a distinction between the type of passenger information available at a ferry port compared to an international airport, officers from Police Scotland’s Border Policing Command work closely with operators at the respective ferry ports to ensure this is a safe environment for passengers who travel as well as the safety and security of communities elsewhere in the UK.”
Mr Anderson said the special importance of the routes was accentuated by the invisible land Border between the Republic and Northern Ireland.
“This requires great trust to be placed on the Common Travel Area arrangements, since a terrorist who has managed to gain entry to the Republic of Ireland (or who comes from the Republic of Ireland) can normally travel to Northern Ireland without passing a border check.”
Mr Anderson also said the frontier between Northern Ireland and the Republic of Ireland was being used by extremists based in the south.
Most dissident republican attacks have targeted the security forces in Northern Ireland.
The Border with the Republic and freedom of movement between Britain and Ireland is coming under fresh scrutiny as the Prime Minister prepares to launch Brexit negotiations.