Originally Posted by
Chronus
Voluntary basis : Assisting police with their inquiries.
Arrest : Formal process to collect evidence which may lead to charge, trial and use of evidence .
The person arrested may have been previously been interviewed informally, ie on a voluntary basis.
Nevertheless the law is most concerned that there should be reasonable grounds for arrest, as the person is detained in police custody for a defined period of time and therefore loss of liberty is involved. Arrest and custody by police is never a pleasant experience, especially for those who have no previous experience of it.
Voluntary interviews are increasingly used to deal with suspects. 'Helping police with their enquiries' is a nice phrase to avoid offending anyone. It's pretty meaningless.