From Cameron’s speech in the Commons (or was it a press conference?), it seems to be because our society is in imminent risk of destruction due to pedophile terrorist scammers, and because several investigations are in jeopardy because the ECJ has declared the current arrangements illegal.
Hmm, I have to wonder why this law wasn’t introduced at committee stage at least when the case was first presented to the ECJ, instead of waiting for the (inevitable, imo) ruling. Rushing it through like this could be taken as betraying a certain lack of forward planning by the ConDems. If I wasn’t steeped in cynicism, that is.