As the band's co-founder Peter Hook explained in an interview:
"What happened was that every club we played in was run by a dodgy promoter in some dodgy part of town. We managed to play in the red light districts of Halifax, Huddersfield, Leeds, Manchester and probably London as well. The police had asked the public to note down the license plate numbers of any strange cars in the area, so they could investigate them later. It was very frightening -- they basically asked you straight out if you were the Ripper."
Although Hook handled his interrogation fine, the band's drummer, Stephen Morris, came off so suspicious that he was taken to the local police station for further questioning. It's always the drummer, isn't it?