I think it would be sufficient to fight against first-past-the-post elections rather than the entire “parliamentary system”. Nick Clegg’s incredible failure to even attempt that is probably going to be his lasting legacy.
I believe Clegg had something to do with bringing about the referendum on this very subject. That at least qualifies as an attempt. nickcleggsfault that the UK electorate missed their once in a lifetime chance to ditch the first past the post system?