In Series 1 Episode 8 of Ashes to Ashes, Gene Hunt gains possession of a video tape which reveals the truth about the car bombing of Tim and Caroline Price.
Acting out of compassion for the childhood version of Alex Drake, he destroys the tape. At this moment the adult Alex Drake gives a warning about the blackmail that will ultimately result from this act.
ALEX: I'm the piece of his past. Or I will be. He'll be blackmailed by Layton for not telling the truth.
What is the nature of that blackmail and how does it relate to the events of Series 1 Episode 1, in which Alex Drake is taken prisoner and then shot by Arthur Layton?