Just because a person did not commit an offence does not mean that the offence did not occur. A person may be arrested for murder as they were seen running away from the scene dripping in blood. If it later transpires that person did not commit the offence but actually administered first aid and then got scared they would be accused of murder and so fled the scene, then they would be released without charge. In this respect, we would still have a crime as the murder still occurred, even if no one else is ever arrested and convicted.
People are definitely innocent until proven guilty, nothing has changed in this respect, certainly not in the Force/department I work in anyway. As for "gross misuse of police powers" - the information we store and they way that it is recorded is set down by the Home Office, we did not make this decision, we follow the rules given to us. On a personal note, I don't agree with it either.
The point of my previous answer is simple, arrested persons now show on PNC even if they are not charged. Whether this information would show on a CRB check I cannot say for definite as I've never had cause to request one. That is why I would suggest the OP obtain a CRB check for themselves so that they can be sure of exactly what is stored.