I am just flabbergasted at the UK... Labour has such an ingrown advantage based where the seats are located. This wouldn't happen in Canada in quite the same way. No way would a party win the most votes yet be third in parliament. Take a look at Quebec in 2007. They had a 3 way race, and the seat totals actually reflected the popular vote. It would be interesting to apply the UNS to that election, and see if the ADQ would have been as short changed as the Lib Dems...
Quebec does actually have some inherent advantage for the PQ in the same way Britain has an advantage for Labour (although for totally different reasons) as the PLQ piles up enormous numbers of wasted votes in seats like D'Arcy-McGee. The presence of the ADQ in 2007 (and to a lesser extent in earlier elections and in 2008) blasted the PQ advantage apart, however, as the ADQ wins more sovereigntist votes than federalist ones.
Anyway, it's mostly because of the ingrained class divisions between Labour and the Conservatives, resulting in Labour seats always having disproportionately lower turnouts and Conservative seats always having disproportionately higher turnouts. There's some slight malapportionment as well, but that's secondary.
Also, Labour would never actually win the most seats while coming third in the PV (unless third meant a result of something like 31-31-30), whatever UNS says.
Oh, I guess the argument would then be that if Labour doesn't win the PV, but wins the most seats, they could say they are representing the people who did not vote...
Anyways, if the Libdems can take votes away from Labour like the ADQ did from the PQ, then they shouldn't be too worried. But I am aware, that we are dealing with apples and oranges here.
I'm trying to understand UK politics more, so forgive my ignorance.
