My client (a self-employed trader) is a retailer who has previously been paying for storage. They have now decided to use the home garage but have had to pay £3,000 for a new garage roof. Their position is that the garage is now used for storage of stock (no longer paying for storage) and that the £3,000 is deductible. I am certain that this expenditure is not an allowable cost, even on an apportioned basis, as it is a repair to a personal asset. If the garage was used exclusively for business purposes, then any such claim would lose the client's principal private residence relief on that proportion of the sale when the house is sold. 

Arthur Weller replies:  

See HMRC’s Business Income manual at BIM37928 (tinyurl.com/2992cwhh). It may be true that the reason this £3,000 was spent was to enable the garage to effectively store stock. However, it is quite likely that if this went to the tax tribunal, they would say that there is a duality of purpose here. Furthermore, if the whole garage roof was replaced, possibly HMRC would argue that this is capital expenditure. See HMRC’s Business Income Manual at BIM35467 (tinyurl.com/bdfa4wsb). Perhaps the answer is to claim it but to explain everything in the tax return and wait for HMRC to challenge.