So I thought I'd try Cooper on dairy in baking. Probably tried it a little bit concentrated but hey least I got a decent/clear cut reaction!
We've sussed out that he can eat stone ground wholemeal flour but no quantity of any other types of wheat flour/products.
We made highlander biscuits with the above flour, so it had the condensed milk & butter in it. Had one biscuit lunch time yesterday. Granted I wasn't home last night but this morning, a

nappy, a bubbly rash with raised skin as well all over the nappy area & his cheeks (face) over the morning developing a lovely red glow with a patched look that develops in a weird rash.
That's enough for me to say nup to dairy for him again for another few months.
Gotta love food intolerances.