Too much rice!
655g was the amount of rice stipulated in the original recipe, when I measured this out it was plain that we would be eating rice for the next fortnight! I have reduced the amount to match the 1 litre of stock (400g of rice)
Method adjustments
The original procedure involved removing the chicken, draining the stock, measuring and re-adding it all back to the casserole.
The amount of stock was exactly 1 litre (so no adjustment required). I have simplified bu just adding the rice to the casserole, which is what I ended up doing anyway.