How is the limit of the Fifth Amendment enforced? What prevents someone from pleading the Fifth Amendment, even if they don't necessarily have something that would incriminate themselves if they answered? Does the opposition have to prove that nothing they say could incriminate themselves to remove the protection? Does the witness have to reveal something to the judge to enforce the protection? Additionally, who knows what random law they might have broken, and might admit to if they testify? Can someone plead the fifth on those grounds?
What prevents someone from pleading the Fifth Amendment, even if they don't necessarily have something that would incriminate themselves if they answered? Immunity. Sometimes prosecutors offer immunity to a witness in exchange for testimony against another defendant. In such cases, the witness cannot claim protection under the fifth amendment because the witness's testimony can no longer incriminate the witness. Does the opposition have to prove that nothing they say could incriminate themselves to remove the protection? No. Proving a negative proposition is generally impossible. Does the witness have to reveal something to the judge to enforce the protection? No, because such a revelation would also tend to incriminate the witness. Additionally, who knows what random law they might have broken, and might admit to if they testify? Can someone plead the fifth on those grounds? Yes. It is not in fact necessary to cite specific grounds for invoking the fifth amendment, because forcing a witness to cite a reason would itself be tantamount to forcing the witness to incriminate him- or herself. Quoting Wikipedia: Truthful statements by an innocent person An incriminating statement includes any statement that tends to increase the danger that the person making the statement will be accused, charged or prosecuted – even if the statement is true, and even if the person is innocent of any crime. Thus, even a person who is innocent of any crime who testifies truthfully can be incriminated by that testimony. The United States Supreme Court has stated that the Fifth Amendment privilege: protects the innocent as well as the guilty.... one of the Fifth Amendment’s basic functions . . . is to protect innocent men . . . who otherwise might be ensnared by ambiguous circumstances..... truthful responses of an innocent witness, as well as those of a wrongdoer, may provide the government with incriminating evidence from the speaker’s own mouth. (Ohio v. Reiner, 532 U.S. 17 (2001) (per curiam)) The U.S. Supreme Court has also stated: Too many, even those who should be better advised, view this privilege as a shelter for wrongdoers. They too readily assume that those who invoke it are either guilty of crime or commit perjury in claiming the privilege. (Ullmann v. United States, 350 U.S. 422, 426 (1956) (footnote omitted)) (Citations inlined)
In a trial by judge (bench trial) that could certainly happen. Most substantial parts of the judicial process can be sealed, under numerous laws and theories. The U.S. FISA "Court" is notorious for operating virtually entirely in secret. Various laws allow for secret subpoenas or warrants, with the subjects on which they are served held criminally liable for violating the court's order for secrecy. In a trial by jury it would probably be impossible for an exonerating fact to be presented to the judge only, since the proper role of the jury is to decide all questions of fact in a case. Furthermore, a court can compel a witness to testify, with no requirement to mitigate the damages of such testimony. However, if the accused knew that an exculpatory fact could be provided by a witness, and that the witness might decline to give (honest) testimony to a jury, he would presumably waive his right to a jury trial, at which point the testimony could (in theory) be given only to the judge.
In a deposition, attorneys are supposed to keep their objections short and refrain from making an objection that indicates to the witness how he should answer. A question might be objectionable because it lacks foundation, because it is compound, because it calls for speculation, etc. Example 2, for instance, could be said to assume that Ms. Redacted was involved, and I might not want my client to discuss how he would act in that situation. Some attorneys in that situation might say, "Objection, assumes that Ms. Redacted had anything to do with this, which you haven't proved, and it's impossible to say what would have happened under circumstances that never happened." This gives my client a pretty clear signal that he ought to make clear that Ms. Redacted wasn't around, and that he should try to avoid getting pinned down on any questions about what he would have done if she had been. This practice -- known as "a speaking objection" -- can be used to signal to the witness how best to answer, and it leads to huge fights in a deposition. To avoid those fights, courts have developed a practice of requiring lawyers to simply "object to the form," rather than coaching the witness. That puts the objection on the record so it isn't waived, and if it's truly problematic, the parties have an opportunity to explain in greater detail after the deposition is concluded.
There are venue restrictions where political speech is restricted, such as on military bases; content restrictions (transmitting classified information to the world); you cannot defraud by saying false things in order to get something, you cannot defame a person, you cannot speak obscenely (though it's hard to tell what counts as "obscenity"). You cannot appropriate other people's property in speaking (i.e. copyright law is a restriction on speech). The type of speech restrictions seem to pertain to speech and violence caused by such speech. A classic limitation is that you cannot speak "fighting words" (Chaplinsky v. New Hampshire 315 U.S. 568), which in 1942 meant calling someone a "damned racketeer" and "damned Fascist", which the court characterized as "inherently likely to provoke a violent reaction". The court subsequently refined its position on "provocative" speech. In Virginia v. Black 538 U.S. 343 a law against cross-burning was found to run afoul of the First Amendment as a restriction on political expression, but it would be fully consistent with The Constitution to outlaw "cross burning carried out with the intent to intimidate". This states may "prohibit only those forms of intimidation that are most likely to inspire fear of bodily harm". The current position is that you cannot incite to the imminent use of force. In Brandenburg v. Ohio 395 U.S. 444, the court stated that the First Amendment does not "permit a State to forbid or proscribe advocacy of the use of force or of law violation except where such advocacy is directed to inciting or producing imminent lawless action and is likely to incite or produce such action". There are myriad laws against threats, for instance in Washington you may not "knowingly threaten(s) to cause bodily injury immediately or in the future to the person threatened or to any other person", and you can't do that ("knowingly cause another to believe that the offender will cause serious physical harm to the person or property of the other person") in Ohio either. You can't get away with threatening "to commit a crime which will result in death or great bodily injury to another person" in California. This class of restrictions on speech seems to be quite robust. You may not induce panic in Ohio, e.g. shout "fire" in a theater -- I don't know if any other state has such a law.
If I want to protest for or against President Trump and decide to wear a Trump mask, isn't that speech protected by the first amendment? Probably. The matter of intent, in any event, is for a court to decide (if the prosecutor determines that the question should even be presented to a court). For example, someone seeking to rob a bank in a mask would probably fall afoul of this law, and it's not likely that using a mask of a political figure would enable a successful first-amendment defense. For a political protestor, it could be easy to show that the intent was to make a political statement and not to conceal identity, in which case it would not be necessary to consider the constitutional question, for a critical element of the crime would be missing. That is, if you say "I wasn't trying to hide my identity," and the court believes you, then you haven't violated the statute. That is a separate question from whether the statute is constitutional. For the law itself to be unconstitutional, it would have to be unconstitutional in every application, generally. If some applications of the law are unconstitutional, the law could stand, but prosecutions for the unconstitutional application would not succeed.
You are correct. A judge may only issue a warrant when it is supported by an affidavit, in which the officer seeking the warrant swears under oath to the facts supporting the warrant. Lying on the affidavit would constitute perjury. But judges very frequently just rubber-stamp the warrants without meaningfully reviewing the affidavits, so the primary form of oversight would be the defendant's Fourth Amendment challenge asserting that the warrant wasn't supported by probable cause. If a judge does review the warrant application and finds the officer's statements not to be credible, he can refuse to sign the warrant, and he is free to also carry that credibility determination to subsequent warrants sought by the same officer or other officers in his department.
I'm not going to comment on the specifics of this law; rather, I think this question shows a misconception of the way the legal system works in general. Here's the question: do you actually have "legally privileged" material on your phone? If not, what's keeping you from claiming that is that it's not true, and lying to a police officer is a bad idea. And just putting a letter from your lawyer on the phone doesn't mean you've established a legal privilege--attorney-client privilege is not a magic spell, it's a reasonable system of protection that only covers certain communications. The bottom line is: the statute in general, and that clause in particular, were included in the law to protect real, important, and substantial legal right. The courts interpret the law in light of that purpose. If the police officer finds a solution that protects your rights while still carrying out the purpose of the statute, the court will be unlikely to fault him or her. In this case, if you tell the officer that there is a letter from your attorney in a particular folder, the obvious solution is for the officer not to open that folder. Problem solved. In practice, in the United States at least, these cases are dealt with routinely; computers are seized, and attorneys and judges work together to ensure that privilege is protected while still allowing reasonable access to seized materials. I would imagine the same is true in the U.K. The bottom line is: the law is not a game, and technical "gotchas" are rarely effective. Common law systems allow judges enough leeway to avoid this sort of pointless technicality.
can you hire a witness as your lawyer to exclude their testimony? That is pure fiction and misleading. Unfortunately scenes like that contribute to keep people ignorant about the law, which then makes it easier for courts to dissimulate their recurrent miscarriage of justice. But Purdue University v. Wartell, 5 N.E.3d 797 (2014) is an example where the Indiana courts did the right thing, and is pertinent to your question. There, Purdue University first assigned an investigator in regard to plaintiff's grievance, and thereafter the University tried to withhold information under pretext that the investigator was also its lawyer and thus that the information was protected by the privilege. Because that person hitherto had been portrayed only as an independent investigator, the Indiana courts concluded that Purdue University was estopped from invoking the attorney-client privilege (as well as the work-product doctrine). Thus, the guy in the film or series who said to be "screwed on Kardashian" reflects pure cluelessness about how the law supposedly operates. I have not seen the plot of that film or series, but the information that the friend-lawyer obtained prior to becoming O.J.'s attorney would not be protected by the privilege because it was not obtained in preparation for O.J.'s defense. If there were one star witness on the opposing side and they happened to be a lawyer, could you simply pay them off by hiring them as your lawyer? This question is somewhat unclear to me, but I will mention that lawyers have a duty to disclose to their potential or actual client any conflict of interests. The rules of so-called "professional conduct" discourage lawyers to ignore conflict of interests in that this conflict may impair their "services". And, as I explained previously, any information that a lawyer obtains as witness rather than as attorney in the matter is not protected by the privilege. Thus, as for If you committed a crime at a law-firm and everyone who witnessed it was a lawyer, is there any rule preventing you from just hiring all of them? the answer is: Nothing prevents the criminal from hiring all of them, but that information is not protected.