Labour won the majority of votes in 1951 though. I think they're pretty savvy about maximising votes now. They've been really astute at winning seats despite a low percentage of votes.In 1945 Labour won a landslide and had a majority of 145. In 1950 this was reduced to about 5. Labour called another snap election in 1951 and the Tories got back in with a majority of about 20. (I think. Must google it!) And that was in the days when party support wasn't as volatile as it is now.
As for the future, I think it will depend on how the Tories shift. If they go further right, they could struggle.