Personally I would not feed dry:
The Truth About Dry Cat Food from Blakkatz

Toxic Pet Food

I feed raw,but always fed wet to my past cats. This is a superior wet pouched food, and I see you're in the UK so you can get it:
Lily's Kitchen • Organic Pet Food, Holistic Pet Care - Certified Holistic Pet Food • Organic dog food recipes • Organic cat food recipes • Lily's Kitchen are ethical producers of organic, holistic, pet foods providing optimum nutr

It has minimum 60% meat, is organic, and grain-free. Cats are not made to process grain carbs, and it damages their health.

It seems like quite a lot of food you're feeding your Tosca, but part of this is that he is growing. The other part is that the food you're giving him is full of filler, and doing him little nutritional good. You will find that with Lily's, or another high meat content, grain-free food, he will feel more satisfied after his meal. If you continue to give him some dry, don't mix it with wet, as this creates a perfect environment for bacteria, even if stored in the fridge. If you switch him to a high quality organic food, you will see differences in his health, the softness of his coat and energy levels. If you thought about switching to a balanced raw diet, you would see even more benefits, including odourless poops, and less of them. His teeth would also get regular cleaning from the meat, and his jaws a great daily work-out.