Would Britain need to block the Kiel Canal physically?

Would Britain need to scuttle a ship in the Kiel Canal to block it?

No. In this scenario, a fortified Heligoland could threaten the canal's useful approaches with guns and destroyers, achieving much of the same strategic effect.

A deliberate blockage inside the Kiel Canal is presented as a possible British tactic but an unnecessary one in this setting. From Heligoland, fortress guns could threaten the nearby channels used by ships approaching or leaving the canal. Destroyers operating from the island extend that control beyond the range of the fixed batteries. The island therefore acts as an external maritime blockade position without requiring a ship to be sacrificed inside the waterway.