The Mayor of London vote will be by first and second preference vote - excellent to see this alternative to first-past-the-post vote! It's much fairer. For example, say 50% felt that the Green party candidate was their preferred, but were worried that any vote other than to their second choice, Labour, would be wasted and give more chance to their least favoured option, say Conservatives. With first-past-the-post, Labour (Khan) would get in again as people worried about Conservative (Bailey) getting in. With first and second preference vote, they would vote Green (Sian Berry) first, followed by Labour, and Green would win.

It's also very easy to count. You simply make piles of 1st choices. If none reach 50%, you take the smallest pile (least favourite) and share their second votes. Continue until one candidate has 50% - which much happen at some point.

Easy to understand, easy to count, still voting for individuals (unlike true proportional representation) and in my view, the fairest system. Let's hope this works well and eventually becomes accepted at general elections.