user: Question: On what date was the lead 8.6%?
Columns: ['Date(s) conducted', 'Cons', 'Plaid Cymru', 'Lib Dem', 'UKIP', 'Green', 'Others', 'Lead']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['5 May 2011', '22.5%', '17.9%', '8.0%', '4.6%', '3.4%', '6.7%', '14.4%']
SQL:

assistant: SELECT "Date(s) conducted" FROM "Table" WHERE "Lead" = '8.6%';