On what date was the lead 8.6%?
CREATE TABLE "regional_vote" (
  "date_s_conducted" text,
  "cons" text,
  "plaid_cymru" text,
  "lib_dem" text,
  "ukip" text,
  "green" text,
  "others" text,
  "lead" text
);
SELECT "date_s_conducted" FROM "regional_vote" WHERE "lead"='8.6%';