There is a general exception to the Data Protection Act for the prevention and detection of crime.
Also one for "historical purposes", i.e. keeping it all forever in case your descendants happen to be interested.
A partial list of exemptions is:
28. National security..
29. Crime and taxation..
30. Health, education and social work..
31. Regulatory activity..
32. Journalism, literature and art..
33. Research, history and statistics.
Together they are - a hole the size of a truck for the authorities.
You didn't think it was there to protect you from the state, did you?