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STV - Terrorists could cross to Scotland by ferry from Northern Ireland, an expert has warned.
Officers at the Scottish ports of Loch Ryan and Cairnryan say passenger information from ferry companies was "incomplete and unreliable", according to David Anderson.
Since 2014 the terror threat in the UK has been rated as "severe", and the former UK independent reviewer of terrorism legislation said the danger is "real and substantiated".
In his last report before leaving office this month, he wrote: "The Canary Wharf truck bomb of 1996, manufactured by the IRA in South Armagh, killed two people, injured more than 100 and caused £150m 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.
Mr Anderson 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," he wrote.
"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."
Mr Anderson 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.
Mr Anderson said the special importance of the routes was accentuated by the invisible land border between the Republic of Ireland 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.