Sorry you are having such a hard time. I think a key reason and why they mention parenting classes is that this does NOT happen at school. That is indicative of more of a home issue. Now, some kids keep it together while at school and then because that is so hard and they struggle to do so, they are their worst selves at home. But this is extreme that it would be unlikely if he has a psychological issue/ developmental issue that he'd be able to hide it entirely from school staff. Have you taken the parenting classes. :>)
I have a son with a developmental delay. We saw an occupational therapist for 6 years. He had many of the issues your son had because he has sensory integration disorder. He did have outbursts and fight or flight responses and often to strange things. To this day, he's 14 now, he will tell me how much he HATES to brush his teeth and does it but I mean, sometimes it is like "pulling teeth" which I tell him we will have to do if he doesn't take care of them! He has had fits over wearing socks in the house, shirts with tags, eating food he feels he can't bare, homework can be a nightmare. But we worked on coping strategies. See, with my son, I realized he was reacting with the tantrums because he was feeling so crummy inside. It gave me empathy. So, I did not react with anger. I adore my son, bad behavior and all and want the best for him. And it would KILL me to write that no one wants to be around my child. Hopefully those in your child's life understand that he's a child struggling and not some evil beast they need to judge (including your mom and other family!).
Truth for all kids, if YOU raise their voice, they will follow. If you smack or are angry or have anxiety or react quickly, they will. So, it is important to no matter what, stay calm. Don't be tempted to yell or anything like that. Some kids actually calm down by deep pressure and asking if you can hug them and giving them a tight loving hug will actually slow down their nervous system.
If your son is saying things that you feel are earnest about his desire to kill himself, seek help. In fact, it might be wise to see a psychologist in general to talk to him. Give HIM an outlet to figure out what is going with no fear of what he says. I would recommend that as your next step.
And I have a cool down/calming strategy that helped my son. I can share that with you if you like?
Does your son get lots of physical activity like running outside, swimming, climbing monkey bars, playing soccer or pee wee football? That type of exercise is excellent at behavior modification!
Sounds like it has been hard. So, after school could he just frankly be exhausted? This may sound crazy but my even keel, easy going second son had monster tantrums when he started first grade. He also wet the bed out of nowhere. I asked his doctor and his doctor said he sounded stressed and over tired. We put him to bed a half hour earlier and let him sleep longer on weekends. We provided support for stress at school (which was just going all day . . . but we provided empathy for that and hugs) and he got over this fairly quickly. It really was that simple for him.
But may or may not be for your son.
Here is something you can try. These are things we did with my older son who has the sensory issues. First, we began talking to him about 'being just right' and just right was how HE felt inside. We gave it a color to identify it, green. They use a picture of a steering wheel with this in occupational therapy. The line straight in the middle I green and 'just right' where a child feels good, calm, relaxed. When they become RED, they are Too Fast (we called it). This is when they are raging, full of energy to where they can not sit still or focus. If they are the other way, they are Yellow or Too Slow which is when they are lethargic, low energy, not wanting to do anything. Knowing how to identify that within themselves is a win. Just right feels best! They will become more motivated to be 'just right' or Green.
Then you introduce strategies that THEY can use. When a child is melting down, you can NOT reason with them and that is not the time. You let them have the bad moments and maybe at best, offer them a piece of gum to calm down (chewing a thick piece of gum slows down the nervous system) but mostly, once it reaches tantrum stage, you have to wait for it to get better. talking to them then is fruitless.
Here is one way to curb tantrums, rage fits. You create a stress thermometer. Draw a thermometer on a piece of paper (the old fashioned kind with the big ball at end and it goes up). The bottom part is green, just right. This is where we want to be. When green, you go through this with him, you are calm, relaxed, smiling, peaceful, hands are relaxed, voice is nice and the right volume and tone, heart beats regular . . . all is well. This is where you want to stay or get back to if you move up the thermometer.
The next section is yellow. At yellow, things are changing. You are feeling a bit irritated, starting to be less reasonable, can't think quite safe, smile is gone, hands are not as relaxed, breathing is a bit heavier, voice getting louder, tone angrier, feeling less in control.
Next section is orange. This is danger zone. You are visibly upset, hands clenched in fists, breathing rapidly, voice loud and angry, heart racing, face scrunched up mad, not thinking straight, not focused, not in control.
Next section is red. This is the full meltdown, rage moment. Totally out of control, hitting, screaming, raging, loss of all reasoning ability.
Then have him really talk about what each one of those feel like to him. Do this on the weekend when he is calmer! Then . . . super important, talk about strategies for what he can do to take it back down the thermometer toward green. If he recognizes he is orange, how can he stop it from going to red? What strategies can you two have? If he is on yellow, how to get to green? Etc.
Kids respond well to this!
Geez, I feel for you. First, this is not a parenting issue (except, that certain parenting strategies will help). I assume that you are somewhere in the good old British Empire with their antiquated mental health system. The problem is that you have been talking to doctors who have no clue. You need to talk to some expert in children's mental health. I think the fact that your brother has Aspergers is a good starting point as your son has a lot of those characteristics.
I do think that you also need to talk to his teachers to get more information about how he is doing at school. You said, "He's good at school , he has been told off for hitting people (which he says was an accident ) and refusing to say sorry, but he's actually quite clever . he rips his homework up before he comes out of school so he doesn't have to do it. Has meltdowns if I ask him to read his reading book . his handwriting is barely legible so has a lot of extra support." I don't think so. He is intelligent and is probably getting good grades (for awhile). But he does not do homework. Has a lot of extra support? and won't read out loud. Those good grades will disappear sooner then later. If the school system sees problems you might get more help. It was early in the year when this was posted and the teachers were still getting used to their kids. If he just turned 8, and is in the 3rd grade he is one of the youngest in this class (size doesn't matter) and that will only make it tougher for him. Third grade (if he is in that grade) is a big transition point (I know being a retired elementary school principal). If your school system is anything like ours, you go from a nice sheltering primary system to the real world and that can be very tough for some kids. So do get in and talk to his teacher(s). Not about how smart he is, but about every thing else. And yes, when he does get home from school, he may be so stressed that the lashes out. So anything physical you can do right after school will be helpful. Unfortunately, with winter approaching, solitary things like swimming and running will be soon out of the picture. Unless, you are down under.
As I said at the top, this is not really a parenting issue. He has some problems that need to be addressed in more places then at home. However, as Specialmom posted, there are things you can do at home to help. I am guessing that most parenting classes deal with problems of kids that do not have special issues. When your child does have special issues...be it sensory intergration disorder, or something like Aspergers, the normal procedures change.
What Specialmom has suggested will help. He needs to be able to express himself and deal with his frustrations. If he does have something like Aspergers he is retreating to a safe place, and he needs to find a safe way out. There are books aimed at his age group which are meant to be read aloud and practiced with him that might help. one is Cool down and work through anger.... https://www.amazon.com/Cool-Through-Anger-Learning-Along%C2%AE/dp/1575423464/ref=pd_sbs_14_6?_encoding=UTF8&pd_rd_i=1575423464&pd_rd_r=1594ab2d-d5bd-11e8-95c3-9923a080f912&pd_rd_w=o3CDA&pd_rd_wg=utKPj&pf_rd_i=desktop-dp-sims&pf_rd_m=ATVPDKIKX0DER&pf_rd_p=7d5d9c3c-5e01-44ac-97fd-261afd40b865&pf_rd_r=AAFFX9S0FS08YWX3NRMD&pf_rd_s=desktop-dp-sims&pf_rd_t=40701&psc=1&refRID=AAFFX9S0FS08YWX3NRMD
You also might want to check out When I feel angry.....
Finally, Dr. Ross Greens book, The Explosive Child, is highly recommended.
Finally, remember you said, "his main triggers are just coming out of school , he's a lot better at weekend , but on school nights he can be a nightmare." That is a key. You need to be working with his teachers to help him make school easier for him. In the States, that would be a 504 plan or an IEP. If 2nd. grade was not too bad for him, have his current teacher talk with that teacher. But, most importantly you need to talk with his current teacher and let her know what is going on. I would also talk with other parents to see how this teacher works. It may be that she is just not a good mix for your son.
Boy, I hope this helps. I really understand how difficult this must be for you. Keep in touch.