alternatehistory.com

1979-1984: Margaret Thatcher (Conservative)
1984-1985: Denis Healey (Labour)
1984: (Majority) def - Margaret Thatcher (Conservative), David Steel (Liberal), Arthur Scargill (Coal Not Dole)
1985-1985: David Owen (Wartime National Government with Labour, Conservatives and Liberals)
1985-1989: David Owen (Labour Majority)
1989-1998: Francis Pym (Conservative)
1989: (Majority) def - David Owen (Labour), David Steel (Liberal), Eric Heffer (Rally of the Left - "Socialist" Labour/Coal Not Dole)
1993: (Majority) def - Neil Kinnock (Labour), Alex Carlile (Liberal), Michael Meacher (The Left)
1998-0000: Peter Mandelson (Labour)
1998: (Minority with Liberal and SDLP Confidence and Supply) def - Francis Pym (Conservative), Jeremy Ashdown (Liberal), Margaret Beckett (The Left)

1980: Denis Healey wins the Labour leadership contest.
1981: Argentine plans to invade the Falklands are temporarily shelved.
1984: With inflation and unemployment soaring, Healey beats Thatcher despite Scargill's left wing splinter.
1985: Argentina invades the Falklands after defence cuts.
1985: Healey resigns and David Owen (who had resigned over the defence cuts) leads a national government, which oversees Britain's defeat.
1989: After losing the Falklands and with the entire left of the party having broken away, Pym's moderate Conservatives win in a landslide.
1998: Mandelson modernises the Labour Party, and wins a plurality at the general election, forming a minority government.


(I feel as if there is more to do with this, but I'm not sure yet...)