Constitutional Renewal

I was extremely concerned to read in yesterday's edition of The Guardian that, according to its political editor, Ministers have already made a decision to introduce alternative voting systems. Can the Secretary of State give me a categorical assurance that that is not the case? Does he agree that he could introduce a new voting system only if he succeeded in a referendum of the British people on the issue, or if his party were re-elected at the next general election having included the issue in its manifesto?