Tories lost 178 seats in 1997.
Tories lost 189 seats in 1945
Labour lost 235 seats in 1931 (from 287 to 52...ouch, just 2 years after the last election)
Tories lost 246 seats in 1906
Funny thing is, these parties were all back in power fairly quickly after such big gubbings. 13-14 years out of power maximum.