Sir Robert must be rotating in his grave at a velocity

sufficient to generate seismic waves. Latest example of 'law enforcement' in (fG)Britain,
According to his blog, our over-tall photographer Alex Turner was taking snaps in Chatham High St last Thursday, when he was approached by two unidentified men. They did not identify themselves, but demanded that he show them some ID and warned that if he failed to comply, they would summon police officers to deal with him.

This they did, and a PCSO and WPC quickly joined the fray. Turner took a photo of the pair, and was promptly arrested. It is unclear from his own account precisely what he was being arrested for. However, he does record that the WPC stated she had felt threatened by him when he took her picture, referring to his size - 5' 11" and about 12 stone - and implying that she found it intimidating.
I have no idea about Britain, but I think it's law in most places in the US that if a plain-clothes officer accosts you and you demand ID, they have to provide it.
Turner claims he was handcuffed, held in a police van for around 20 minutes, and forced to provide ID before they would release him. He was then searched in public by plain clothes officers who failed to provide any ID before they did so.

Following his release, he further claims that the police confirmed he was at liberty to take photographs, so long as - according to the PCSO - he did not take any photographs of the police.
If it's not law in Britain, it would at the least be courtesy for someone in plain clothes to show ID before searching you, to prove A: they really are cops and B: therefore have a legal backing of some kind for the search. However, as noted by my title, they seem to have forgotten Sir Robert's Principles completely.

Further down,
This is just the latest in a long line of PR disasters that have dogged police forces over the last 12 months, with tourists, schoolboys and passers-by all subject to arrest for the heinous offence of pursuing their hobby. Each incident is followed by much police hand-wringing, and statements to the effect that these are one-offs: the fault of over-zealous individual officers.
Except that if it keeps happening, it ain't just the 'over-zealous' officer; they're either not getting the word, or they're getting the message that they can keep doing this and get away with it.
The Home Office has issued numerous statements reaffirming the public’s right to take photographs. Last week, the Met issued its own guidelines, which may go some way to explaining why the Police so persistently get it wrong.
You really need to read this to get the full effect of the idiocy involved. I will quote a bit from the response they finally got from Kent police:
"At the time of this incident, a police officer responded to a report concerning a man who was taking photographs of buildings and people in Chatham town centre. When challenged by the police officer the man refused to give any personal details which it was thought was suspicious.

"As a result, he was arrested and asked to wait in a police vehicle while his details were checked. He was released a short time later after these details had been properly verified, and no further action has been taken.
And we're back to, among other things, did the first two ID themselves as police? If not, why the hell not?

I'm now going to post Sir Robert Peel's Nine Principles of Policing(thanks to Lawdog for keeping track of them); see if you can figure out how many these people are violating in the cases listed in the article:
1) The basic mission for which the police exist is to prevent crime and disorder.

2) The ability of the police to perform their duties is dependent upon the public approval of police actions.

3) Police must secure the willing co-operation of the public in voluntary observation of the law to be able to secure and maintain the respect of the public.

4) The degree of co-operation of the public that can be secured diminishes proportionately to the necessity of the use of physical force.

5) Police seek and preserve public favor not by catering to public opinion, but by constantly demonstrating absolute impartial service to the law.

6) Police use physical force to the extent necessary to secure observance of the law or to restore order only when the exercise of persuasion, advice, and warning is found to be insufficient.

7) Police, at all times, should maintain a relationship with the public that gives reality to the historic tradition that the police are the public and the public are the police; the police being only members of the public who are paid to give full-time attention to duties which are incumbent upon every citizen in the interests of community welfare and existence.

8) Police should always direct their action strictly towards their functions, and never appear to usurp the powers of the judiciary.

9) The test of police efficiency is the absence of crime and disorder, not the visible evidence of police action in dealing with it.