alternatehistory.com

1979-1988: Margret Thatcher (Conservative)
def. 1979: Jim Callaghan (Labour), David Steel (Liberal)
def. 1983: Michael Foot (Labour), David Steel (Liberal), Roy Jenkins (Social Democrats)
1988-1993: Neil Kinnock (Labour)
def. 1988: Margret Thatcher (Conservative Party), David Steel/David Owen (Liberal/Social Democratic Alliance)
1993-1995: Norman Tebbit (Conservative)
def. 1993: Neil Kinnock (Labour), Alex Carlile (Social and Liberal Democrats), David Owen ('Continuity' Social Democratic)
1995-????: Gordon Brown (Labour)
def. 1995: Norman Tebbit (Conservative), Alex Carlile (Social and Liberal Democrats), Malcolm Rifkind (Unionist)

So the idea is that the Falklands never happens, and without the patriotic surge 1983 isn't such a big victory for Thatcher. The Brighton Bomb attack is subsequently butterflied, with the Conservatives winning 1983 without the big increase (instead doing around 30% of the vote and 340 seats). Kinnock subsequently wins the next election, and runs the Country about as well as expected. Tebbit becomes Tory leader, and wins the next election on a 'law and order' campaign, and slips in with a narrow majority. The majority quickly erodes, with Brown coming in and winning a respectably large majority whilst the Scottish wing of the Conservative Party just up and leaves.