John De Lorean hawked the car around a bit, including Ireland, the Irish government looked at his plans and laughed him out of the country.
The Thatcher government was desperate to try and solve the unemployment problem and of course the "troubles" in Northern Ireland at the time and took every word De Lorean spoke as gospel.
Belfast had at the time a large base of highly killed ship builders, and it was thought by politicians that this skill could be transferred into car manufacturing, despite there being no real history of car building.
Its not that the workers from Belfast were lazy or incompetent - they were just being asked to throw away a lifetime experience in ship building and start all over again in car manufacturing.
There was a very good BBC documentary about the De Lorean repeated shortly after his death, focused on the man and the company as well as the car and the film.
As for building the cars in Britain, i have to disagree with you.
Britain had, and still has, a highly skilled base of small car manufacturers pumping out exotic, individual and mostly expensive small production run sports cars.
It was simply that the British government at the time wanted the big investment in an low employment and scarred Northern Ireland.