That is our wonderful voting system in all its glory. You can see why the 2 major parties don't want to change it.

Year Government seat majority vote share
1979 Tory                43   43.9%
1983 Tory               144   42.4%
1987 Tory               102   42.2%
1992 Tory                21   41.9%
1997 Labour             179   43.2%
2001 Labour             167   40.7%
2005 Labour             66   35.2%

The other worrying trend is the fall in the turnout.
1945 to 1997 turnout never fell below 71.4% (1997). Highest was 83.9% (1950)

Since 2001 the turnout has never been above 70%. Lowest was 59.4% (2001) and the highest was 68.8% (2017)