Which rectangular flag centred with a white square was flown by British ships as a sign that it was due to sail?

Question

The Red Ensign, a flag that originated in the early 17th century as a British ensign flown by the Royal Navy, is currently specifically used by which group?

Answer 1

Blue Peter
Blue Peter is a British children's television programme that was first broadcast in 1958. The programme, which has had continuous seasons since it was first aired, is now the longest-running children's TV show in the world. It is currently shown live on the CBBC television channel. The show's content, which follows a magazine/entertainment format, features viewer and presenter challenges, competitions, celebrity interviews, popular culture and sections on making arts and crafts items from household items.