A legal bid to compel Boris Johnson to reverse plans to suspend parliament before Brexit has begun at the High Court in Belfast.
Victims campaigner Raymond McCord is seeking an urgent injunction aimed at forcing the British Prime Minister to change his advice to Queen Elizabeth to prorogue the House of Commons.
Mr McCord's lawyers claim he received assurances that no such suspension would take place ahead of the October 31 deadline for the UK to leave the EU.
They argued that the government's move to put parliament on hold for up to five weeks represents an unlawful attempt to thwart MPs from debating a potential no-deal Brexit.
Ronan Lavery QC told the court: "My client watched the events which took place yesterday on television with some dismay.
"There had been a response from the prime minister's solicitors saying there's no basis for an undertaking to be given... in relation to his request that parliament not be prorogued in advance of EU Brexit day.
"Then yesterday happened, which seemed to be at odds with not an undertaking, but an assurance there was nothing to worry about."
Mr McCord, whose son Raymond jnr was murdered by loyalist paramilitaries in 1997, is mounting a wider legal challenge against any withdrawal from the EU without an agreement.
The Belfast man claims a departure on those terms would breach the Good Friday Agreement.
According to his legal team the use of prorogation is also unconstitutional, with the policy posing a threat to the peace process.
With the prime minister pledging the UK will leave the EU on October 31 "do or die", the judicial review challenge is listed for hearing next month.
However, the application for an injunction was lodged after Mr Johnson announced plans to suspend parliament.
"It's an unprecedented prorogation," Mr Lavery contended.
Pressed by Lord Chief Justice Sir Declan Morgan to identify an unlawful use of the power, counsel alleged an ulterior purpose.
"It's to impede the amount of parliamentary time that is available to debate," he said.
Adjourning the application until tomorrow, Sir Declan requested amendments to the papers.
Outside court Mr McCord claimed a no deal Brexit could have dire consequences.
"This could wreck the peace process," he claimed.
"I want the court to clearly state this is unlawful, and that what Boris Johnson is doing isn't for the good of the country, it's for his own agenda and to try and sideline parliament."
His solicitor, Ciaran O'Hare of McIvor Farrell, added: "As has been predicted by police, politicians and commentators, such a policy is likely to lead to economic turmoil, if not long term recession, and medicine and food shortages.
"Indeed, the likelihood of civil unrest in the circumstances must be high, as well as a raising of sectarian tensions between groups in Northern Ireland.
"The delicate constitutional balance which has thus far been achieved, will be destroyed."
