OK, to explain "first past the post" (FPtP). It means that in each area the candidate with the most votes wins that seat. So in an extreme case with 3 candidates they could be distributed in proportions 34%/33%/33%, with the first getting in with only just over a third of the vote. The problem is that while Labour and Tory have a lot of geographical 'safe' seats (ones where they have a big majority) the LibDems tend to be more evenly distributed. This means that Labour and Tory are likely to divide up the majority of seats betwen them and LD left with only a few.
Take some hypothetical seats:
Tory Labour LibDem Result
40 30 30 Tory
30 40 30 Labour
45 20 35 Tory
=== === ===
115 90 95
As you can see from that, LibDem get more votes than Labour but no seats at all. Project that across 650 seats (and add a few minority parties who will take votes and not get any seats at all)...
no subject
Take some hypothetical seats:
As you can see from that, LibDem get more votes than Labour but no seats at all. Project that across 650 seats (and add a few minority parties who will take votes and not get any seats at all)...