Thanks for the link - it was long but very readable.
Here is the summary of why the courts decided against the government:
----
a) [s1 of DRIPA] does not lay down clear and precise rules providing for access to and use of
communications data retained pursuant to a retention notice to be strictly
restricted to the purpose of preventing and detecting precisely defined serious
offences or of conducting criminal prosecutions relating to such offences; and
b) access to the data is not made dependent on a prior review by a court or an
independent administrative body whose decision limits access to and use of the
data to what is strictly necessary for the purpose of attaining the objective
pursued.
----
My personal interpretation of the reasoning in the ruling is that while a more broad data _retention_ framework is OK for practicality reasons (i.e. it is not practical to know in advance that a person is suspected of a serious crime, nor is it practical to restrict retention to only such persons as it may be necessary to look at data of other people as part of an investigation targeted at a person suspected of committing the serious crime), it must be accompanied by protections at the _access_ level (i.e. such access must be tightly restricted and judged to be necessary by a qualified independent body based on the facts of the specific case).
Here is the summary of why the courts decided against the government:
----
a) [s1 of DRIPA] does not lay down clear and precise rules providing for access to and use of communications data retained pursuant to a retention notice to be strictly restricted to the purpose of preventing and detecting precisely defined serious offences or of conducting criminal prosecutions relating to such offences; and
b) access to the data is not made dependent on a prior review by a court or an independent administrative body whose decision limits access to and use of the data to what is strictly necessary for the purpose of attaining the objective pursued.
----
My personal interpretation of the reasoning in the ruling is that while a more broad data _retention_ framework is OK for practicality reasons (i.e. it is not practical to know in advance that a person is suspected of a serious crime, nor is it practical to restrict retention to only such persons as it may be necessary to look at data of other people as part of an investigation targeted at a person suspected of committing the serious crime), it must be accompanied by protections at the _access_ level (i.e. such access must be tightly restricted and judged to be necessary by a qualified independent body based on the facts of the specific case).