The vet told me to try this and the problem seems to be resolved: Apache would always eat too fast, and couldn't tolerate it, he was retching after 2 minutes of eating. At the moment though it seems that this new food is tolerated quite well.
Hill's I/D dry food is great, they are helping my cat a lot with chronic diarrhoea. The diarrhoea is in control, our cat hasn't lost any weight, and is growing in spite of everything. The food is clearly helping to normalise the intestines which have become inflamed.