I accept that this is extraordinarily unlikely however imagine a few changes
First The ICE patrol ship stays in the Falklands and there is no South Atlantic War
Secondly Owen wins the SDP leadership and manges to cause a real crisis with Liberals, perhaps that no Liberal supporting independent nuclear disarmament be allowed to be a candidate
Thirdly Thatcher pushes further right policies, perhaps proposing a Poll Tax in a 1984 election.
Is there any chance that there would be an attempt to prevent a Labour Parliamentary Majority (based on perhaps 38% of the vote 35% Conservaiv 13% SDP,10 % Liberal 4% Other) Actually exercising power