Parliamentary systems still devolve into two-party contests in each district though, it's more that the larger number of districts means that regional parties sometimes takes one of those two slots. At their peak the Lib Dems basically only ever won MPs from a few small regions of the country, mainly Somerset, Sheffield and London. The Greens have their one MP in Brighton, and then the other parties are all regional.
That's a lot to do with their policies though. The Greens are not really different to Labour, Lib Dems ... I don't think even they know what they stand for these days.
A better recent example was UKIP. A single issue party that managed to accrue enough of the vote that they got their issue implemented without ever having to win an election. In FTFP you can implement massive change in politics, without needing to actually replace one of the big parties.
