Between 1922 and 1981, only members of the Parliamentary Party were eligible to vote for the leader and the deputy leader.
At the 1981 Labour Party conference, in what was seen as a major democratic advance for the left of the labour movement, the voting procedure for the election of party leader and deputy leader was altered. The electorate was extended to include nominations for members of the constituency parties and trade unions. MPs were given 30% of the vote, the constituencies 30% and the trade unions 40%.
At the 1993 Labour Party conference, on the initiative of the new party leader John Smith, voting procedures were altered to (supposedly) introduce the principle of ‘One Member One Vote’. Trade unions and constituency Labour parties were required to ballot their members individually, with results being allocated proportionately. The weighting of votes in the electoral college was also changed to give each section (PLP, CLP and TU) a third of the share of votes.
The union intervention in last year's election was decisive in securing victory for Ed Miliband.
Yet, almost two decades and three party leaders later, Miliband has emulated John Smith by further diminishing the trade union share of the electoral college to 30%.
Perversely, under the new arrangements the per capita vote of each of the (say) 50,000 non-paying registered supporters sharing 10% of the vote will be worth significantly more than the per capita vote of the almost 3,000,000 levy-paying trade unionists sharing 30% - by any definition this is a retrograde step.
NB an excellent House of Commons Library briefing from October 2010 outlines the evolution of leadership elections in the Labour Party since 1922 as summarised above:
http://www.parliament.uk/briefing-papers/SN03938.pdf
TC