Speech Delay?

Oscar's speech is somewhat of a concern to us at the moment, mostly in terms of pronunciation.  I'm pretty confident that he doesn't have any issues with language as he understands what we say, he points to thinks and tries to name them and repeats what we say.  The words he can say he uses in context and he signs quite proficiently to make his needs known.  He has started creating his own signs which, with a lot of pointing and guesswork, we are starting to figure out.  I'm not sure where he's getting them from and often can't see the link - for example, he touches his two index fingers together to sign"play dough".  Just in the last few days he is starting to really try and repeat words, although none of them sound like what he is trying to say.

I'm going to use this post to detail, for my own benefit, where he is at the moment so that I can see his progress and get things in some sort of order for his 2 year review with the Health Visitor.

WORDS HE CAN SAY WELL:
Mama
Yeah
No
Owl
Papa
Nana (Jenny)
Pepper

WORDS HE CAN PARTLY PRONOUNCE
Ball, book, bin, bird, box, bath, bear, Bing, bounce, bus - he says "ba" for all of these
Banana - "nana"
Shoes - "oo"
Gone - "ga"
He's very recently started saying "mo" for moon and mouse too

WORDS HE STRUGGLES WITH (AND WHAT HE SAYS INSTEAD)
Daddy - "gaggy"
Help, please, van, car - he says "ba" for these too
Bye, done, ta - "ga"
More - "nor"
Lawnmower - "nor-no-ner"
Hedgehog - "ge-goh"
Badger - "ga-ger"
Digger - "giga"

He struggles to make vowel sounds other than "ah", "oo" and "ow".  He only has "b", "g", "n" and "m" as consonants but they sometimes get mixed up too - for example, he says "ba" for everything but then says "ga" for bye which should be easy for him. 

He makes a lot of animal noises and they mostly sound like what they're meant to although he does say "ba" for "quack" and "mmm" for "moo".

He also says "gmm gmm gmm ba" for Stick Man, gingerbread man, Postman Pat... sometimes with more or less "gmm" noises but always basically with his mouth closed, like he's really having trouble forming the words.

Nobody else understands much of what he says and they don't understand the signs either but he gets by.  We don't leave him with anyone except nursery and occasionally Ant's parents (Jenny is quite good at understanding him).  He's having a lot of tantrums and that's probably because he's frustrated that he can't say what he wants to and we often don't understand him. 

He says "ba" for pretty much everything, usually accompanied by a sign or pointing so we know what he's getting at.  Unless he comes on phenomenally in the next six months I'm expecting he'll need some sort of speech therapy.  He comes on in fits and starts but his pronunciation doesn't improve - he said virtually nothing by 18 months except "daddy" and "owl", not even "mama", but then he had a spurt of learning lots of words.  It slowed down again but he's currently trying to repeat every thing and getting a lot more communicative, however his pronunciation still hasn't improved.  I'm determined to advocate for him as I genuinely believe knows the words and is of average, if not above average, intelligence so I don't want to see him struggle and give up.

I'm going to see his Key Worker at nursery about it tomorrow so will be interested to see what she says!