What is torture? what are classes of offence or person created by law?

The law can create a legal fiction. The monarch - The King or Queen is a legal fiction. The prime minister is a legal fiction. Why? they are created by the law.

It may be beneficial to understand classes of criminal cases where individuals charged have a charge changed from the norm. Murder and Treason are an example. To murder a Judge is not Murder, it is Treason, to Murder the monarch or the monarch’s direct family is not murder it is Treason. The murderer is no longer a murderer he is a Traitor. The class of person caused by the offence, upon the victim, as a class of person. Likewise, the sentence changes. No class of people are above the law, however so high, the law is above you.
If a member of the public was to murder a bus driver, the murderer would receive a tariffed life sentence. The second less obvious class of case is the murder of a police officer doing his duty. The sentence imposed is often a 30-year tariff. If it was premeditated, with no remorse, a whole life sentence tariff would be passed. This was put in place to protect police officers doing their lawful duty. This is right and a deterrent.
The Criminal Justice Act 1988 section 134 was an act of parliament that created a “class of offender”. That is to say the class of offenders were state officials acting as state officials at the time of the offence. The class of offender if convicted is called a torturer. A torturer is the enemy of all mankind. Torture is often misconceived as to extract information, in fact it is defined wider than that, to include coerce or intimidate and the coercion and intimidation does not have to be the claimant it could be those around the claimant. All state officials including police constables are crown servants. If a member of the public was to beat, wound, kill, cause severe pain or suffering to an individual other than a monarch or judge he or she would stand charged as normal charging or indictment.
However, if a police constable committed these offences acting as a police officer and many have. The crime changes to torture. For a reason. For example, GBH with attempted section 18 becomes torture if the arrest is unlawful or the level of violence used is unlawful. Likewise, malicious prosecution becomes “causing suffering” suicides on bail are often the result. To protect the public from the few hundred rogue constables and to act as a deterrent. It was not the intention of the act to give immunity via paragraph 135. But immunity they have. Bear in mind last year 23 members of the public were killed after or during arrest 5 of which died during restraint, hundreds have died since 1988 with no access to justice approximately 560 deaths 3500 serious unlawful violence in 35 years. There are hundreds of violent incidents perpetuated each year by the police, some causing the death of detainees. There is no known test for this indictment. Not a single police constable since 1988 has been indicted. This looks like immunity.

These are worth reading.
https://www.supremecourt.uk/cases/docs/uksc-2011-0115-judgment.pdf

https://www.supremecourt.uk/docs/speech-150618.pdf

https://www.supremecourt.uk/docs/speech-131015.pdf