Allowable expenses (sometimes referred to as revenue or trading expenses) are anything which has been purchased “wholly and exclusively” for the use/purpose of your business.
This means that any expenses must have been used for either the purpose of day to day running (e.g. stationery) or expanding (e.g. advertising) your business.
Therefore, the item should only be claimed where it is 100% used for the business - however you may be questioned during an audit as to the usage of the item.