I will be speaking to a new client of mine to ask for a rough estimate of mileage or at least a percentage of business/personal use of his car as he has dropped off some receipts including fuel/service receipts.If he suggested that he used it pretty much 50:50 between the two, that would be enough for me and I would allocated 50% of the fuel/service/road tax costs etc. It is so small an amount, I don't think it would ever be inspected but I expect that what is good enough for me isn't good enough for HMRC. I doubt that the client could or would provide a mileage log so I don't know whether to just do this and mention to him that one day HMRC might want to see back-up or not bother. I don't suppose he would need to agree this with HMRC either (?) but at the end of the day we aren't talking a lot of money. He actually doesn't think he can claim that much and so isn't bothered, but I think it is a waste of a normally allowable expense. If he did suggest 50:50 would you guys use this to allow these expenses as suggested.......and.......in the section in the tax return where it asks if there are any estimated figures would you describe this allocation? In fact, in what circumstances has anyone used this section of the self-assessment?
I would accept a 50:50 split, especially if the household has another car assuming he works in a sector where he actually does business mileage. I think you would be wise to suggest he keeps a log book to corroborate his claim and then in the event of an inspection at least you would have covered yourself. No need to mention this as an estimate, in fact I think if you put down something is an estimate you would need to re-submit the return once actual figures are determined.