Parliamentary Voting System and Constituencies Bill

On the issue of turnout, there were referendums in Scotland and Wales, introduced by the Labour Government in 1997, and proposals by the Labour Government possibly to consider referendums on the European constitution and the single currency. Indeed, in the last Labour manifesto, there were proposals for a referendum on the alternative vote. Where was the mention, at any point in any of these referendums, of a threshold being applied?