Oh I should add, it doesn't matter if materials cost is not claimed as an expense in the same year as an item is sold. HMRC will understand that craftsmen may buy bulk material and use it for years.
As Dibs-h said, stop doing what you are doing, if you are audited you may find yourself in a heap of trouble as they may well cancel large parts of your expense claims from past years.
I keep mine simple, I have a printed receipt for every expense I claim, if HMRC want to check they are welcome to. The fact that I may not have used all those materials yet is none of their concern.
As Dibs-h said, stop doing what you are doing, if you are audited you may find yourself in a heap of trouble as they may well cancel large parts of your expense claims from past years.
I keep mine simple, I have a printed receipt for every expense I claim, if HMRC want to check they are welcome to. The fact that I may not have used all those materials yet is none of their concern.