Average Change in by-elections 1950 - 2010
1950 - 1951: Con +7% Lab -2% Lib -5%
1951 - 1955: Con -1% Lab -1% Lib +1%
1955 - 1959: Con -9% Lab +1% Lib +7%
1959 - 1964: Con -14% Lab +2% Lib +14%
1964 - 1966: Con +1% Lab -2% Lib Unchanged
1966 - 1970: Con +7% Lab -17% Lib +3%
1970 - Feb 1974: Con -12% Lab -4% Lib +9%
1974: Con -1% Lab -3% Lib -2%
Oct 1974 - 1979: Con +10% Lab -9% Lib -5%
1979 - 1983: Con -11% Lab -11% All +18%
1983 - 1987: Con -14% Lab Unchanged All +12%
1987 - 1992: Con -12% Lab -1% Lib Dem Unchanged
1992 - 1997: Con -19% Lab +7% Lib Dem +5%
1997 - 2001: Con -1% Lab -9% Lib Dem +4%
2001 - 2005: Con -4% Lab -19% Lib Dem +15%
2005 - 2010: Con +3% Lab -11% Lib Dem -1%
2010 Parliament so far: Con -8% Lab +9% Lib Dem -7%
had no idea the libdems were that underwhelming after 2005