rather than talking about David M missing an open goal, I think it is all Len McCluskey's fault. As the Gen Sec of Unite the Union, he supported Ed Miliband and turned, I would perceive, the Union vote behind him. Good old Len is also probably the principal supporter of Jezza.
One union leader doesn't have that much power any more - the union block vote went in 1993. No, David M lost because he was lousy campaigner. His brother spoke better and worked harder at pulling in uncommitted voters.