I use my own (private) van for my secondary occupation. I drive from home to the customer. I carry my work clothes and tools specifically in my van. I have not included my car in my business. As it is an old car, I do not intend to do so. Can I still claim my fuel costs (with fuel card and invoice) and what percentage of private/work use can I justify? I estimate 80% work transport and 20% private. Do I need to be able to substantiate this?