How democratic are the reformed electoral systems used in Britain’s devolved governments and English mayoral elections?

As part of our 2018 Audit of UK Democracy, Patrick Dunleavy and the Democratic Audit team examine how well citizens are represented by the two main reformed electoral systems used in the UK – the ‘additional members system’ (AMS) and the ‘supplementary vote’ (SV). How successful have they been in showing the way for more modern electoral systems to work well under British political conditions?