Influencing / challenging parties from the right/leftWatch
I think the best way to do this is to selectively target safe seats of your chosen party which have a problematic MP and mount s challenge there.
Fir example if I was the leader of a Socialist Party wishing to push labour to the left I would look at targetting a Labour Safe Seat with a right leaning MP rather than attacking Tory seats or labour marginals.
Immigration was raised by both parties in 2015, and I doubt this would’ve happened as prominently if UKIP weren’t polling 10-20%.
It’s the reason that we had the EU Referendum, because Cameron had to appeal to the UKIP voters or risk a Labour government. So in this context, UKIP and other eurosceptics got what they wanted without getting any actual power.
In essence to have any influence a rival needs to get a hot button issue but in the long run our system and electorate is not desperate enough for change. We are a constitutionally small c country.
I've been on the fence about FPTP for a while now but I'm starting to starting to edge towards some sort of PR maybe an Additional Member System like in Scotland.