It depends on how you define 'win', we should remember that a switch from stable majority to stable majority has only ever happened once since the war and Major's majority was huge. Simple things like avoiding the victory party in Sheffield prior to the election, perhaps some slightly dodgier stuff like Major's affair with Edwina Currie being leaked, make Maastricht less of a success etc and you have a scenario where Labour can govern to some extent with the help of the Liberals, the SNP and the SDLP. But a stable majority really would require something like an earlier black Wednesday.