Its tactics flopped in places such as Oxford but gained traction in Northern Ireland, said Barber, who investigated archive material for a pending book about UK-wide film censorship.
The Democratic Unionist party rejects any deal that would treat Northern Ireland differently lest this weaken the union with Britain.
It was screened in England, Scotland and Wales but banned in Northern Ireland after opposition by local councils.
Drawing on archives at the Public Records Office of Northern Ireland, Barber uncovered an energetic censorship campaign by local authorities that overrode decisions by the London-based British Board of Film Classification.