Re: This goes to show one thing
"But the Conservatives are vulnerable to protest parties at times"
_ALL_ parties are vulnerable to swing and non-voters.
The mistake they make is to only court the swing voters (marginal seats) and treat non-voters as "If you don't vote, you don't exist" - all parties get lists of _who_ voted even if they don't know what they voted for and it's been made abundantly clear to me that regular voters get more door knockers. Most parties don't even bother trying to campaign to people who haven't voted.
A solid campaign based on getting those who haven't voted out to the polling booths would be a fundamental shock to the conservatives on all sides as they rely on electoral complacency.
Whilst this might sound like a pipe dream, it's exactly the tactic that Barack Obama used to mobilise the Democratic vote in the USA.