Generally speaking, not many teachers are "tooled up" to deal with gifted kids. Especially kids who are not conventionally/academically gifted. It's a shame, but it's true.
Gifted kids are sometimes bullied and excluded, mainly because kids his age are frequently not his true peers. He has ideas and interests the kids his age simply can't understand. (And what other time in life are people expected to be grouped strictly according to age? It's really ludicrous!) The best things you can do are to teach him how to cope with this treatment--find other "loners" to befriend and stand up for one another (since having someone speak up on your behalf drops the incidence of bullying by something like 80% according to one study I read! One kid is easy prey, two aren't worth the effort...), crying makes it worse, etc.--and to help him find his true peers. These true peers may be significantly older than he is, but share common interests and skills with him. Gifted kids sometimes don't have lots and lots of friends, especially if they are more introverted and respond better to 1-on-1 interactions. But that's okay! He needs a handful of people who "get" him, not to be the most popular child in school. Find a few friends and his situation will improve.
I know nothing about the state of gifted education in the UK, so I can be no help for you there beyond to suggest that you do some research. Here in the US, programs and opportunities for gifted kids vary from state-to-state, even from school building to school building. Subject acceleration, grade skipping, schools devoted entirely to gifted kids, and home schooling are all potential options here, depending upon your luck and the area in which you live. These might be things to consider for your son.
Talk to the teacher about his strengths and weaknesses and what she thinks might work for him (but remember that you are the best expert on your own child!), consult with the principal/headmaster about possible options available, even check with the superintendent of your local school district--maybe another school in the area has a better track record on gifted education.
Be sure to talk to other parents of gifted kids in your area. What's being done for their kids? There may even be a local support group for parents, in part to offer the very advice and comfort you require, but also in part to help parents to advocate for changes and programs to benefit their kids. Seek it out. If we have them here, there's probably something like them there.
Your son sounds like a gifted child, and not the compliant kind if the work he's given bores him. (I was a compliant gifted kid; my son, who appears to be significantly more gifted than I ever was, isn't compliant. Compliance is no indicator of anything except compliance.) But non-compliant behavior can make it more challenging to get him the help he needs, because many, MANY people assume gifted kids can just learn anything and everything should be easy for them. But gifted kids have special needs, as surely as a child who falls at the other end of the bell curve has special needs.
Gifted kids think differently, learn differently, need stimulation that's often very different from what they receive in a standard classroom. You will have to advocate for your son if you want to 1) teach the schools what they need to know to help your son, and 2) stand up for what's right for him. It's not easy. It's often a battle.
You might consider having him tested, preferably by someone with experience and expertise in testing gifted kids. Walking into the school administrators with ability and achievement tests in hand can sometimes get people moving better than simply saying "My son is gifted" will. Not always, but sometimes. Administrators like numbers. It can also give you some indication about what your son's specific needs actually are, though again, you are the best expert about your son. Test scores are just another bit of information to help you make decisions.
You're among friends here. You're not alone, and neither is your son. I wish I knew more about the state of the UK's gifted education so that I could point you in some useful directions, but all I can give you is generic advice. Start researching now for those specifics, and don't stop until you find something that works for your son as a whole person. (That's key!) You may have to think creatively and do things differently than everyone around you. (I'm currently home schooling my son, something I never thought I would do!) But if it works for your son, you'll feel it's totally worth all the swimming upstream that you have to do to get there! Promise!
All the best,
K-
