@LiefievdM, thanks again :)
Yes, I think we'll approach his nursery with a perspective of, "Can we have a look at the IEP and a chat about it to make sure that we're doing the same kind of things at home" perspective rather than a "We know our rights and we're going to perform our own audit"... They're actually really good and we're lucky to have them on our side so the last thing we'd want is to alienate them.
Also, good advice RE SN playgroups or coffee mornings etc, I'm embarrassed to admit that's something we hadn't really thought of!
Our little chap has a great nature, he's just turned 3 and where-as he does have some language and can name some things in books, ask for drinks/food etc and sings nursery rhymes pretty much constantly there's no verbs, just nouns. He can't converse with us and won't say hi or bye to anyone. Seeing him in a nursery setting brings home how far behind he is, and it's worth mentioning they've held him back a year too... No sensory/food or sleeping issues but some tiptoe walking, hand flapping and spinning round is present and he seems to struggle to sit still or concentrate for anything over a few minutes, he's always on the go! Also very little in the way of joint play, shared experiences or bringing things to show us etc.
My wife has a history of some autism in her family and her nephew at our childs age was told by his nursery that they couldn't cope with him for any more than one hour per day as he was so angry and frustrated and pretty much spoke his own language that no-one (Including his parents) could understand. Fast forward to now and he's fourteen, in mainstream school and actually doing some of his GCSE's early! When I speak to him these days I'd honestly never guess that he was on the spectrum if I didn't know. He's a lovely lad an everytime I'm around him he fills me with enthusiasm and positivity. Also, a great book I read is 'Send In The Idiots' by Kamran Nazeer, he didn't speak until he was four, attended an Autism based SN school and ended up working as a government advisor and author, again something really encouraging and insightful.
Thanks again for your responses here, as you say it's great to touch bases with folk in a similar situation. The internet, for all it's ills really can be a force for good at times :)