Oooh, I have just been looking at old elections stats - had completely forgotten the impact of the SDP in the mid 80s elections, before tactical voting was even thought of. SDP and Labour combined still had a smaller percentage of the vote than the Tories but I wonder how many seats were lost to the left by the split vote?
1979: C 43.9%, 339 seats; L 36.9%, 269 seats; Lib 13.8%, 11 seats (turnout 76%)
1983: C 46.0%, 362 seats; L 26.7%, 148 seats; SDP 12%, 3 seats; Lib 14.3%, 10 seats (turnout 72.7%)
1987: C 46.2%, 358 seats; L 29.5%, 155 seats; SDP 10.2%, 3 seats; Lib 13.6%, 7 seats (turnout 75.3%)
1992: C 45.5%, 319 seats; L 33.9%, 195 seats; LD 19.2%, 10 seats (turnout 77.7%)
1997: C 33.7%, 165 seats; L 43.5%, 328 seats; LD 18%, 34 seats (turnout 71.5%)
2001: C 35.2%, 165 seats; L 41.4%, 323 seats; LD 19.4%, 40 seats (turnout 59.1%)
2005: C 32.3%, 197 seats; L 35.2%, 356 seats; LD 22%, 62 seats (turnout 61.3%)
Cam, there have always been more votes against the Govt than for it (since 1979 at least, I didn't look back any further) and the ones who can't be bothered shouldn't be reckoned in.
(from electiondemon )