Re: No accountability
At the time of the arrest, the police officers had reasonable grounds to suspect that a warrant was outstanding, based on the information available to them at the time.
The fact that the information was wrong is irrelevant; the grounds for arrest simply need to be objective and an officer needs to be able to articulate them.
"You're under arrest because I believe you have an outstanding warrant"
"Nah, bruv. I was in court two days ago"
<insert custody systems check>
"Ah, so you were. Sorry about that, enjoy the carnival!"
Harassment, for ease of reference, requires a course of conduct and an intention to harass, and there's a general exemption for people acting in good faith.