Two top lawyers have warned of a legal nightmare after being told of plans by the Executive to break ranks with London's Same-Sex Couples Bill.
They are Professor Brice Dickson, the director of Queens University's Human Rights Centre, and Rosemary Craig, a University of Ulster family law expert.
Both were given details of a Legislative Consent Motion (LCM) which has been obtained by the Belfast Telegraph after being circulated to ministers. It seeks to accept parts of the Marriage Bill but reject its major provisions.
Prof Dickson warned of a "legal minefield" with test cases likely, while Ms Craig predicted that children adopted by same-sex couples would suffer the most.
"These proposals would swamp our family courts, both magistrates and county level, with jurisdictional issues," Ms Craig said.
"Initially there will be great uncertainty on how to proceed and then there will be test cases. This is going to cost a lot in financial and human terms."
The Department of Finance and Personnel (DFP) is responsible for family law. Its minister Sammy Wilson has forwarded the LCM to his Executive colleagues along with a 15-page memo.
It seeks to treat same-sex marriages contracted in Britain or elsewhere as civil partnerships.
It is, in some ways, the gay equivalent of marriage but does not convey the right to adopt. Anyone in a civil partnership here cannot adopt a child even as an individual. Ms Craig warned of problems if people in gay marriages who adopted children elsewhere in the UK moved here. Prof Dickson, a barrister, believed that in practice courts here might recognise the adoptions.
He added: "This is a complex area of private international law and I doubt if the Executive have their own experts in that field."
Mr Wilson was advised by the London Department for Culture, Media and Sport that the European Convention on Human Rights would accept Stormont's right to make law in line with local opinion.
Prof Dickson believed that this principle held in many circumstances, but could be challenged.
"It is accepted that social change should generally go in tandem with the wishes of the vast majority in a jurisdiction. But that argument weakens when the question is family status and personal sexual behaviour. At a certain point the majority is not able to dictate to the individual."
He pointed out that local views in Northern Ireland were invoked by the Government to justify keeping homosexuality illegal here in a 1980 test case. Despite this argument the court found against the Government.
In his memo Mr Wilson mentions that some other cases, such as same-sex marriages in the armed forces or at British consulates and sex changes, will not be fully covered in Northern Ireland law. He suggests these issues should be left until they come up.
Westminster is likely to introduce same-sex marriage but the Executive is resisting. Here same-sex couples are allowed to enter civil partnership but not adopt. In GB unmarried couples of whatever sex can adopt children, but here only single people or married couples are allowed to. A test case overturned this ban on unmarried couples earlier this year. It is being appealed.