The idea
Somebody taking photos of policemen, or of Guards on parade, or of the Palaces of Westminster are NOT terrorists, nor are they in the vast majority of cases even remotely involved in terrorist activities. Being arrested for such activity is stupid.
Repeal these unnecessary and probably unintended by products of the Prevention of Terrorism Act
Why is it important?
People will gradually become scared to get out of bed each day in case some innocent activity can somehow be construed as participating in or contributing to an act of terrorism.