In terms of Party Systems, how Diverse does FPTP make it? (EX)

-FPTP will not allow Extremists Parties into the System, like the BNP which got a 500K Votes, but 0 Seats -But FPTP prevents New Parties getting in and makes Political Intertia [Maintaining the Status Quo of the 2 Largest Parties having the only chance of Winning] UKIP got Support across UK in 2015 GE with 4 Million Votes, but only got 1 Seat.