Hello, I was arrested and detained in a police station.

I was given an appropriate adult even though I objected as I was 23 years old.

This appropriate adult also happened to be my elder sibling who I do not like at all.

I didn't know at the time that he was working for the police(SOCA).

I am sure that this is illegal, can you please clarify what the law is in relation to this as I am unhappy about it?(for obvious reasons)

What do you mean by you were given an "appropriate adult?" You are of legal age.

Laws vary. Where are you?

We also need to know more details. Were you released in his custody? Did he pay the bail?

I am in UK(London)

I was in the cell for 4 days under section 18. On the 4th day I was told that my solicitor had arrived. I went into the room and my elder brother was hiding behind the door.

He told me that they were going to get me(the police) and that I had to have an assessment of my mental state.

I was interviewed by a doctor who said that I was suffering from hypermania and that it is normal as I had been locked in a room for 4 days without speaking to anyone.

My sibling, who unbeknown to me, was and officer for SOCA(the English FBI basically) was made to be my appropriate adult in my interview.

We do not speak and have never got on. I objected but he was still allowed to come into my interview.

I was 23 years old.

I was put on remand in prison awaiting trial.

Why was having your brother in the room upsetting to you? Did your family not realize you were arrested?

Do you have an Attorney? Did your brother's presence in any way influence what happened at the Hearing?

I wanted to know if an officer of the law who is also a family member can act as your appropriate adult in the UK?

Many strange things have happened and I have never spoken to him again, he avoids me. Would you say that it is normal procedure?

Sorry here in the US there is nothing even similar to an appropriate adult, in fact after over 20 years in law enforcement I have never even heard the term.

It appears from looking it is someone appointed or accepted to have authority over you, if you have limited mental ability. So if they deemed you, or you have been deemed as not able to be mentially fit, then they will accept somemone over you. Or of course anyone who is a minor would be appointed one

Also of course the Police can lie to you about what evidence they have, and other things,

Their role is only to be sure you have been properly taken care of and to explain to you in words you may understand if you have limited understanding what is happening to you. They are also to tell other family members you are there.
It does not have to be a family member but can be.

Agree with FrChuck - from what I can find the brother was appointed as some sort of mental health guardian. I also see nothing that prevents that from happening.

If a person's competency is being questioned that person has little say in who/what/where - and it appears that that is what happened here.

Have you spoken with a social worker or mental health worker in order to get your brother removed from that appointment?