While you can't entirely compare it (as some people would have probably voted differently under a different system) it still gives an indication.
My guess is if the UK had a proportional system some of the smaller parties (e.g. Greens) would have more seats (as people currently don't vote for them as in most places it's a wasted vote) while most of the larger parties (Tories, Labour and also the SNP) would have fewer seats, in some cases significantly.
Fully agree. Unfortunately I don't see that happening any time soon. In particular the Tories and now to a lesser extent Labour stand too lose too much power by moving to proportional representation, so I don't see them supporting that for the foreseeable future.