I double checked my pattern cutting and cross referenced it with a different book...and hey presto I now have a collar I am much happier with. It involved re-setting the neckline lower and opening out the collar line.
So I didn't start modifying the jacket itself, noooooooooooo...I have learnt through years of messing things up that you should test it out first! So here is how the modified calico looks (see open and half closed):
Looking good. Happy to move on now.