I can only speak for my force, but you are asked if you want a solicitor a) when you're booked into custody, b) when you're booked out for interview and c) at the start of the interview itself. Police can't advise whether people get a solicitor or not, but they are offered one several times. When being booked in you are also asked if you want to phone anyone.
If someone gives an alibi during interview, it's perfectly acceptable to probe it, as shock/horror, people do lie unfortunately. What your friends son may have deemed aggressive questioning may have just been in depth questioning around his alibi to ensure there were no holes, or bits that didn't add up. The other side of this is someone has been assaulted, and harsh though it is that your friends son has been arrested when he didn't have anything to do with it, the police do have a job to do, and need to be satisfied as to any involvement.
They aren't allowed to lie, but I do wonder if they might have phrased it like someone else suggested, eg if there was CCTV, would you be on it, or could you explain it. I've asked questions like that myself many times. The officers would be pretty stupid to lie, all interviews are tape recorded, and the master copy is signed by the suspect and sealed up so no one has access to it unless it goes to court. I'm not going to deny there are corrupt officers, sadly there are corrupt people in all professions, but to do something like that would be daft. The majority of us want to keep our jobs and not be suspended with a gross misconduct charge hanging over us.
I wonder if he was so "frightened" he may have got the wrong end of the stick, or just interpreted things wrong. For what it's worth, if someone seems particularly scared or upset, or is a first timer in custody, I will always explain things in mega detail, make them a cuppa, and check if they want a solicitor. However, whilst I think I am a pretty nice interviewer, I still have to ask lots of questions to make sure everything is covered, and I'm sure some people are upset by that. Turn the tables and put yourself as the victim of a crime - I'm sure if someone was arrested for a crime against you you would want to know that a very robust interview was carried out, to either confirm guilt or innocence. I would hate to have it in my conscience that an innocent person was charged with an offence, but similarly get frustrated when a clearly guilty party isn't. A lot of the time we're dammed if we do and dammed if we don't, and that relates to lots of parts of our job.