asked Her Majesty's Government:

Whether they will provide, in respect of each mayoral election which has taken place using the supplementary vote system (a) the number of votes cast and percentage turnout; and (b) the number of votes in each case which were not transferable at the second stage, due to (i) no second choice made; (ii) second choice made for the same candidate as the first choice; (iii) second choice made for the other candidate progressing to the second stage of the count; and (iv) uncertainty or other reasons.[HL4449]

This information is not held centrally by the Government.