For the first time, two women will be elected in the seven-strong constituency section in a ballot based, also for the first time, on one member, one vote.
The outcome will be a further test of how far Mr Blair's views are represented among Labour's 250,000 party members after he won 58 per cent of their votes in the leadership contest.
Margaret Beckett, who is standing for the five-strong women's section, is expected to romp home, with most interest focusing on the constituency section which, unusually, has three vacancies after the election of Tony Blair and John Prescott as leader and deputy, and the departure of Neil Kinnock to Brussels.
MPs expect Gordon Brown, Robin Cook, David Blunkett and Harriet Harman to retain their seats, with the leading candidates to join them including three more members of the Shadow Cabinet - Mo Mowlam, the national heritage spokeswoman; Chris Smith, who covers green issues; and Jack Straw, who heads up local government and housing. All three were prominent in organising Mr Blair's campaign and their election would see all seven constituency places held by Shadow Cabinet members. Their leading challengers, all more from the party's left, include Dennis Skinner, Peter Hain and Dawn Primarolo, Labour's shadow health minister.
Mr Hain, the former Tribune group chairman, is campaigning against the strong hold Shadow Cabinet members have on the executive, arguing that Labour's ruling body should have voices from the grassroots. Mr Skinner, who takes the same view, is standing again after losing his executive seat two years ago. Mr Benn, after his defeat last year, is not standing.
The new election system makes the result more difficult to call as, under the old process, whoever won a constituency's vote won all of it, a method which understated support for less favoured candidates. Their backers hope that will boost the chances of Mr Skinner or Mr Hain defeating Mr Straw or Mr Smith, or of Dawn Primarolo taking one of the two places reserved for women. Against that, however, all-member ballots, which take the vote beyond the most active members, appear to have favoured those with the high profile that a Shadow Cabinet post makes easier to achieve.