I once thought that something should be deducted from profits before tax is something that should not be adjusted in the proforma to get tax adjusted trading profit. But I do not think I am right. For example, pre-trading expenditure can be deducted at the first year of trade, which needs to adjust(deduct from…), I just wonder if I have a right view.
Sorry but I am uncertain what you mean in your first sentence above. I would propose simply learning the rules as given – see OT notes chapter 4, or otherwise can you try to explain what is your query above?