When Brazil's military dictatorship wanted to ease off and restore civilian government, in a controlled way, in the late 1970s, it licensed two officially-permitted parties to compete, PDS and PMDB.
One was safely "right", the other safely "left", so that the exercise could have the show of democratic choice.
The Labour Party's easing-off from Blair-Brown dictatorship has taken a somewhat similar route.
Five candidates are now in competition, but three of them only just scraped the ridiculously high minimum of 33 MPs' nominations.
Evidently the dominant factions in the Parliamentary Labour Party decided to use "spare" nominations to allow "licensed" left-wing (Diane Abbott) and right-wing (Andy Burnham, Ed Balls) candidates to enter the contest along with the front-runners, David and Ed Miliband.
Left-wing Labour MP John McDonnell had been backed by the Labour Representation Committee, the Bakers' Union, the rail union RMT, Unison United Left, and Unite United Left. The CWU, Compass, LabourList, Save The Labour Party, the Fabians, and the biennial Policy Conference of Labour's biggest affiliated union, Unite, had called for all declared candidates to be on the ballot paper.
But the generalissimos of New Labour decided to have their own choice of left candidate, rather than the left's choice.
Now, from 10 June to 26 July, unions and local Labour Parties can make “supporting” nominations.
Ballot papers will be posted out to Labour Party and affiliated-union members from 16 August. The election will be by transferable vote (i.e. you vote 1, 2, 3, 4, not just an X for your favoured candidate). The ballot closes on 22 September. Anyone who joins the Labour Party before 8 September can vote. The result will be announced on 25 September.
Affiliated union members have one-third of the voting power, local Labour Party members one-third, and Labour MPs and MEPs the other third.