What is demand and refusal? the leading case?

If a bailor demands return of goods and the bailee refuses, that is actionable as a breach of contract > Howard E Perry v British Railways Board - plaintiffs were steel stockholders and stored them with the defendants. a strike of steelworkers meant no steel would be moved and the Board agreed/supported the workers. it was held that due to the Board refusing the bailor to see their property, this would be an action in conversion