“In this instance, we can achieve legal certainty by restricting the definition of a ‘qualifying civil partnership’ so as to exclude civil partnerships which were entered into in Northern Ireland,” she added.
It comes after comments made by Mrs Foster last week, in which she said she had no recollection of sending such a letter.
“This is another pretty serious memory lapse, given it is on an issue which she claims to be of such importance to her own party,” said Mrs Long.
“It appears Arlene Foster was not across every jot and tittle on this matter, as was the case with RHI. This was not routine correspondence but from a Minister to a Minister in another Government.
“It is disappointing enough this letter was sent but then to try to deny any knowledge of it only adds to that disappointment. The DUP has always resisted any progress towards full equality for LGBT people and these letters now show that, not content with doing so here, both she and Simon Hamilton sought to interfere in the matter in another jurisdiction as well.
“The DUP may have a mandate to oppose equal marriage here but they certainly don’t in Scotland.”