So I took him in for the vet who saw him on Saturday to re assess him for follow up and repeat bloods. There's no real signs of a blockage - he pooed normally this morning - and no indication of kidney issues.
My thoughts are that this to do with his diet and gut health - I did a bit of searching yesterday, I know Google isn't always our friend but I like to think I am discerning enough not to jump to conclusions. What I did learn was the importance of differentiating between vomiting and regurgitation, something those of you with experience of dogs with digestive issues will know about I'm sure. And Oddy was most definitely regurgitating - undigested food coming back out and no heaving, therefore not coming from his stomach. To my mind he eats a lot of grass, while to some degree it's normal behaviour and the old adage that they do it when feeling unwell is not necessary so, it did seem excessive. But then, he's an excessive kind of boy! Even so, there is some evidence suggesting it can be connected to gut health.
So I made the vet aware of these things (no mention of Google) suggesting that he could do with something to tempt his appetite given that he rejected his kibble last night, and I came home with a tray of tins of Hills Prescription diet. I really hopes this helps him turn the corner, he's also on Omeprezole which may or not be a good thing.
Cass and I have come home now as my son and his OH are there for a few days, so he will be in good hands.