I think that restriction only applies if law enforcement collects the info illegally. That isn't the case here, this is a private individual or group. Any lawyers here know???
I'm not one, but this point occurred to me after a mull-over:
If evidence obtained illegally by a private citizen is admissible, then a private citizen could beat a confession out of a suspect and the confession would be admissible. Evidence obtained by aggravated assualt is illegally-obtained evidence.
Were this legal, the police would have picked up on it a long time ago. All a police officer would have to show in court was that (s)he didn't suborn any such beating.
If the info was on a government (UK) server, the government (UK) already possessed that information! The information will not be tainted if prosecutions proceed. The ‘release’ of the FOIA data merely exposed the information to public scrutiny. The information shows the illegal actions to evade FOIA and destroy government property (data, code, email...)