Stormont has "no duty" to comply with an order from the Secretary of State to implement abortion laws in Northern Ireland, the High Court has heard.
The argument was made during a legal challenge to a move by Secretary of State Brandon Lewis to press Stormont to formally roll out abortion services.
The region's once-strict abortion laws were liberalised in 2019 following legislation passed by Westminster at a time when devolution had collapsed.
Stormont's Department of Health has yet to centrally commission full services due to an impasse within the devolved administration.
This led to the UK government introducing new powers to allow Mr Lewis to intervene on the devolved issue to formally direct Stormont to begin the services.
He used the powers to direct ministers in Belfast to take the steps necessary to deploy abortion services across the region, with a deadline of the end of March 2022.
The Society for the Protection of Unborn Children (SPUC) is seeking a judicial review of regulations introduced earlier this year.
They contend that Mr Lewis exceeded his legal authority when he granted himself an unprecedented level of control over abortion policy in Northern Ireland.
Acting for SPUC, Northern Ireland's former attorney general John Larkin QC told the High Court that there is an "absence of any duty on any person to comply with the directions".
He said there is an "absolutely fundamental lacuna" in the regulations, and referred to a "screamingly obvious" gap in the law
"Not only is there no sanction or enforcement mechanism, but more importantly, we say, there is no creation of a duty to act in accordance with the direction," he told Mr Justice Colton.
"Has he (Secretary of State) been given the power to impliedly amend the Northern Ireland Act? We say that he hasn't.
"A minister of the crown cannot boss people about unless the law gives them power to do it and act in accordance with his edict, and this doesn't.
"The Northern Ireland Office may wish such a provision had been made, it may be bitterly regretting it now, but in these regulations, as it stands, there is no obligation to comply with them."
The hearing is expected to last for two days.