How democratic is the Westminster ‘plurality rule’ electoral system?

In the first part of our 2018 Audit of UK Democracy, Patrick Dunleavy examines a topic of foundational importance for any liberal democracy – how well does the electoral system (in this case the Westminster plurality rule, aka ‘first-past-the-post’) convert votes into seats? A sudden growth in two-party support in 2017 allowed the UK’s ancient voting system to work far more proportionately. But is this outcome a one-off blip, or the start of a new long-term trend?