You can hear the excitement in Jan Siewert’s voice when Jadon Sancho’s name is mentioned but the story that springs most readily to his mind about Manchester United’s new £73 million signing has less to do with a daring dribble or jaw-dropping goal or any other show-stopping turn on the pitch. It was Sancho’s reaction to being told he would not be allowed to play in the knockout rounds for England Under-17s at the World Cup four years ago because Borussia Dortmund, who had signed him from Manche


