user: Question: when was the episode on which Barbara Windsor and Heston Blumenthal guest starred broadcasted
Columns: ['Episode', 'Broadcast date', 'Guest(s)', 'Singer(s)', 'Ratings']
Types: ['real', 'text', 'text', 'text', 'text']
Sample row: [1.0, '14August2012', 'Michael McIntyre and Alex James', 'Amy Macdonald', '1.44m']
SQL:

assistant: SELECT "Broadcast date" FROM "Table" WHERE "Guest(s)" = 'Barbara Windsor and Heston Blumenthal';