For centuries British mps have been elected on the winner-takes-all system: the candidate with the most votes in each constituency goes to Westminster as its representative. The result has been a strong two-party system, with the winning party usually able to form a government with a working majority in Parliament.
But the SDP-Liberal Alliance has now given notice that the price for its support in any future government will be a fundamental change in our electoral system. It wants to introduce a form of proportional representation to make the composition of the House of Commons more clearly reflect the spread of votes in the country.
Would Labour or the Conservatives ever agree to it?
David Jessel talks to Eric Heffer , mp, The Rt Hon David Steel , mp, The Rt Hon Enoch Powell , mp, and analyses the results of a special opinion poll.
Producer JAMES HOGAN Editor PETER IBBOTSON