 When this plurality in favour of the unions was first introduced, it received considerable criticism from the more social democratic wing of the party.It transpired that if the unions had had an equal share to the PLP and the membership then Healey's narrow majority would have been wiped out and the more left-wing Benn would have won the contest.The challenge for the deputy leadership of the party came a year after the election of Michael Foot as leader, which had seen the party shift to the left and resulted in a split which had created the SDP, who in turn had formed an alliance with the Liberal Party to appeal to centrist voters.