The thing for me is that the police misused the law and quite blatantly so as well. Even the former Lord Chancellor who brought in the idiot law says so.
This is the same as all the other idiot terrorism laws that were deliberately misused outside of their original intention. For example, the quite draconian surveillance laws that were brought in specifically to allow government agencies to monitor suspected terrorists were used within 4 months of it becoming law to monitor people dropping litter or allowing their dogs to mess in parks. It's cynical politicking done by the government of the day to do as they see fit, they throw out the terrorism or child porn hysteria to get a stern law passed, opponents are accused of being soft on terrorists or kiddy fiddlers, but then use it for things that would never have been passed if proposed to Parliament.
Can you imagine any government getting a law passed that would allow the police to detain someone who hasn't committed, or reasonably been suspected of committing, an arrestable offence, confiscate every bit of electronic equipment from them, demand their email and social networking passwords then tell them not to change them anytime soon then refuse to tell you what they intend to do with all that data or whether you'll ever get your equipment back? That'd never get through Parliament. What actually passed as law was a limited provision to allow police at borders to detain people to investigate whether they were "preparing, instigating or committing terrorism", a big difference that's been hidden by some as "if you've nothing to hide, what's your problem?"
What can we do about it? Very little. The state does as it sees fit but occasionally gets pulled in by the ECJ or ECHR for excesses then it spins it via friendly, anti-Europe, press about these nasty Europeans interfering with our ability to deal with nasty people.
Don't get me wrong, we're not living in a tin-pot dictatorship with rigged elections but it leaves a nasty taste in the mouth to see our elected officials deliberately misusing laws and allowing the state body of the police to misuse them as well.