Poor training does not a police state make
Its a shame that what could have been a fairly innocuous incident was spoiled by apparently poor training/knowledge on behalf of the police.
Of course we'll discount the possibility that the photographer might be egging the pudding and that there were no other relevant factors at play and he was as amiable and cooperative as he infers.
It is right that, unusually, the powers the police have for stopping and searching under terrorist legislation do not require reasonable grounds to exercise their use. You can get upset about this if you want but thats the way it is. Other legislation also provides a power to require someone to provide information as to their identity and movements, again requiring no suspicion of any offence. Failing to do so IS an arrestable offence.
What is often confused is that GROUNDS for an arrest are not the same as NECESSITY for arrest.
But based on the story as presented the necessity of the arrest seems to be the issue here. Ironically though you can be "detained" for as long as is necessary to search you, or ascertain your identity and movements which would have amounted to the same thing but not technically been an arrest as such under law.
In all likelihood the police at the time responded negatively to being photographed and used the "gathering information likely to be of use to terrorists". An unkind person might argue that annoying the police was the intention of the photographer by taking their picture in the first place.
Yes the police have made a mistake and yes I suspect rather than admitting it have tried a bit of FUD instead. But in the interests of balance I would say this. I suggest that the majority of people do not like to be photographed and I have come across many who believe it is illegal to do so. If you doubt it, walk up to a stranger getting into their car and take a picture of them and see what happens.
Add that fundamental dislike with the paranoia of the polcie about terrorism and complex legislation and its hardly surprising that this will happen. But that comes back to my first point that Kent police themselves (eventually) admitted, training is key.
I have my own views about WHY you get by default such corporate bollocks from police forces nowadays. But that would just be ranting...