I agree with Dame Margaret that the reasons Labour lost are more complex than may first appear.
However, the most obvious aspect, clear to anyone with eyes and ears, is that Ed Milliband was a massive part of the reason why Labour lost.
I believe that the majority of the electorate ignore the minutia of policies and promises, and simply decide if they like the party leader or not.
In this case of Milliband, he was a public-face disaster for Labour, he we was inarticulate, odd, geeky, inarticulate, frightened, unconvincing, clumsy ... the list goes on, but any of them make him unattractive, and all of them make him toxic.
And this time - again regardless of policies, Labour have managed to re-incarnate Michael Foot, a principled fair man, but you wouldn't trust him to walk your dog round the block.