CREATE TABLE table_28793 ("Episode" FLOAT, "First broadcast Denmark  (  DR1  ) " TEXT, "Official TNS Gallup ratings" FLOAT, "First broadcast UK  (  BBC Four  ) " TEXT, "Official BARB ratings" FLOAT)

When was the first UK broadcast for the episode with an official TNS Gallup rating of 1575000?
SELECT "First broadcast UK ( BBC Four )" FROM table_28793 WHERE "Official TNS Gallup ratings" = '1575000'
SELECT "First broadcast UK ( BBC Four )" FROM "table_28793" WHERE "Official TNS Gallup ratings" = '1575000'