In an ATL where the Ulster Unionists remain in the Tory caucus, could one of their own acceed to the party leadership and eventually No 10? POD 1970.
More or less ASB barring some sort of Cabinet wipeout in a terrorist attack leaving the NI secretary the most prominent member alive.
Maybe not in the '70s, but why not closer to the present day? To make it easier, we could set the POD at 1960. I'm guessing that NI has to be as close to "a region like the others" as possible (no Troubles) for this to work...
Collins has been approached by both the Conservative Party and the Ulster Unionist Party to run for Parliament, though has not made any commitment to either party. During the 2005 Ulster Unionist leadership election he was cited by a number of prominent Ulster Unionists as an outside figure who would make a good leader, but Collins declined as he felt he had "no experience of politics."[17]