Rather exasperatingly, Ordnance Survey Northern Ireland don’t provide a way for their maps to be embedded into websites! (Nor do Ordnance Survey Ireland.) It’s something I’ve looked into a few times but I haven’t yet managed to find a solution.

Thanks for letting me know - much appreciated :-)

To my knowledge, the GB Ordinance Survey does not operate in Northern Ireland. Northern Ireland is part of the Republic of Ireland's operation.