VAT reclaim on supermarket purchases

How do we treat the VAT element on say, a Tesco receipt when some items are zero rated and exempt and others are standard rated? It would be a very time consuming exercise to calculate it all manually. Also, how does it work with food purchased at a supermarket? I have a small food manufacture client who regularly buys ingredients from supermarkets for New Product Developement, some raw and some pre-prepared etc. Is there any VAT to reclaim on this?