The British government is coming under pressure to assure people in Northern Ireland that they will not be given lesser protection against external terrorism as a result of moves toward electronic borders.
At the same time, former Ulster Unionist leader now Conservative peer Lord Trimble has urged a Schengen-type agreement between the British and Irish governments in order to preserve the existing Common Travel Area.
London and Dublin are in regular discussions about the implications for both countries of the British government's plans to secure its borders with both sides seeming to agree that this move need have no implications for the land Border between Northern Ireland and the Republic.
Until now unionist attention has focused on the politically explosive possibility that an e-border around Britain could see British citizens from Northern Ireland uniquely required to produce identification when travelling to other parts of the UK.
DUP leader the Rev Ian Paisley is still awaiting assurance from prime minister Gordon Brown that this will not be the case.
However Lord Trimble and Ulster Unionist peer Lord Rogan have turned the spotlight on how Northern Ireland is to be protected against any international terrorist attack, given its physical detachment from the rest of the United Kingdom. There have already been arrests of persons living in Northern Ireland with suspected al-Qaeda links.
As a seat of devolved government and now home to a new MI5 headquarters in Holywood, Co Down, Northern Ireland plainly cannot be discounted as a potential target in ongoing British assessments of threat levels.
In the House of Lords on Wednesday, Lord Rogan asked security minister Lord West for an assurance "that the same quality of protection against external terrorism will be afforded to citizens of the United Kingdom residing in Northern Ireland as to our fellow citizens who reside in the mainland".
Lord West replied: "The quick answer is yes. We are making sure that is exactly what happens."
However, Lord Trimble was not reassured, and accused Lord West of failing to understand "the basic concept" after "a slip" - subsequently corrected by the minister - in which he referred to people travelling from Northern Ireland "to the United Kingdom".
Lord Trimble had earlier asked Lord West if, in their discussions, the Irish Government had pointed out that British citizens comprised the largest group of foreign nationals in the Republic.
Lord Trimble said that they, together with hundreds of thousands "if not millions" of Irish passport holders living in Britain, were accustomed to travelling back and forth between the two states "without any formalities ever since the creation of a separatist Irish State".
Anticipating the "considerable inconvenience" to them likely to result from e-borders, Lord Trimble asked: "Would it not be much better to take the existing informal common travel area and put it on a formal basis analogous to the Schengen agreement that applies elsewhere in Europe?"
He added: "This would solve the problems that arise in practice and relieve the difficulties experienced by the Home Office, which seems to be intellectually challenged by the idea of a land frontier."