Also worth better highlighting is that a major part of the 40% rule controversy was that it was 40% of the registered electorate (including those not *able* to vote as well as those choosing not to). Some allowance was made for this http://www.scottishpoliticalarchive.org.uk/wb/pages/referendum/1979/40-rule/electoral-roll.php, but it is argued that that flies in the face of normal democratic protocol - those not voting are not counted as voting one way or another and are deemed to be accepting of the result of those who *do* vote.     