[member=2128]Womble[/member] Your accountant is right and, like you, I always think that splitting a cost/expense is more straight forward than paying your business for personal use of, in your case, a trailer. However, there are circumstances when "paying" for your personal use might be better: e.g. you claimed for trailer as a 100% Annual Investment Allowance item and then use it for a once in a life-time tour of Europe - Honest John would declare that and show a biz receipt for "rental".
HMRC know/expect that small sole-trader businesses will have some shared-use assets: therefore, because I do my own accounts/self-assessment, I make sure to summarize shared costs and adjustments etc etc on my tax return so that HMRC know (should a human actually read my return) that I know what I'm supposed to be doing and am, more than likely, applying accounting/tax rules correctly.