Whoops yes I can see I missed quite a lot of vital info out of my OP. Sorry for the drip feed!
DS is 4. We live in Denmark so the setup is a bit different too. He has been having speech therapy for 6 months. I wanted to get him started sooner, when he was still at the childminder (0-3 go to CM, 3+ is kindergarden) but they said that his speech would probably blossom in the first 6 months at kindergarden. It didnt.
He had ear infections just after his first birthday and had drains put in (dont know what they're called in English) and has been checked regularly by the ear doctor. Last time was 6 months ago, the drains had fallen out, she checked his hearing and it was ok.
I am getting his hearing checked again soon.
At the meeting they mentioned that DS usually has a runny nose, so it might be that he has had a build up of fluid in the meantime, that it might be happening and clearing up without us noticing, as SuiGeneris mentions.
At the meeting they also mentioned I should discuss with the ear dr a referral to the hearing clinic, where they do more detailed tests in different spaces etc.
I've had a quick look at selective mutism, and I dont think it's that, as it affects people who are capable of speech, and DS isn't very clear, and doesnt talk much at all. He is also bilingual - English and Danish (which believe it or not are actually quite closely related). But here in Denmark they dont have quite the same experience with bilingualism as we do in the UK. Since the start of november he has started chatting to me a bit more, telling me what he can see on the way home, the weather, what's in the sky etc.
I have started an email thread between his nursery worker, the speech therapist, ccing in the nursery boss, so there is a record.
They didnt exactly say that it is a MASSIVE PROBLEM but they were quite clear that he doesnt play with others in the the way that they would expect a child of his age to. I've noticed that when we pick him up in the afternoon and he is playing inside, he is usually alone, occasionally with the 3 other boys from CM, but if he is outside he is playing with others on the trampoline or on the bikes. There is a very big emphasis on getting children to be social here. It's as important as learning to read and write, possibly more so.