Re: facial recognition
"You are under arrest on suspicion of assault."
That doesn't tell him why they suspect him of assault, which assault or the evidence that led to the arrest. No process breach.
In the UK the police can hold you without charge for a period (24 hours minimum, more in relation to some crimes) and have no obligation to tell you why, or to answer your questions.
Do you know that he didn't get a phone call, that he wasn't able to engage a lawyer?