Parliamentary MPs returned under FPTP
SNP: 1,454,436 votes / 56 seats / 49.87% popular vote / 25,972 votes per seat
Conservatives (inc. Speaker): 11,340,398 votes / 331 seats / 37.83% popular vote / 34,261 votes per seat
Labour: 9,331,617 votes / 232 seats / 31.13% popular vote / 40,222 votes/seat
Plaid Cymru: 181,704 votes / 3 seats / 12.13% popular vote / 60,568 votes/seat
Obviously the SNP and Plaid have a big advantage because they concentrate their efforts on seats in their respective countries and probably should be considered as a separate bloc.
The can't-really-complain brigade
LibDem: 2,415,862 votes / 8 seats / 8.06% popular vote / 301,983 votes/seat
Given that they were always going to be up against it after cosying up to the Tories, they did remarkably well, all things considered. If they hadn't spent the last thirty years shoring up their targets, they'd have been wiped out completely. 8 seats was a good result.
The losers set up to lose
Green: 1,150,809 votes / 1 seat / 3.84% popular vote / 1,150,809 votes/seat
UKIP: 3,862,740 votes / 1 seat / 12.86% popular vote / 3,862,740 votes/seat
The most striking thing here is that if Labour had backed the Lib Dems on the AV vote in 2012 (and won) then the Conservative party wouldn't have a majority of any description (nor would anyone else, but it does seem in retrospect a very poor decision on Labour's part). It's impossible to tell how the election would have turned out under AV - as there isn't any data - but it couldn't have delivered a Conservative majority under any circumstances. You can pretend to know where the second, third, etc. choices would have gone, you can make a guess, but no more than that. Point is, it would have given a hung parliament.