If you take a lot of business trips and want to include your spouse or partner, a proportion of their travel costs can probably be claimed back for tax purposes, says Carl Bayley in Business Tax Saver.
But only if their presence is required for business purposes – for example, if your spouse has a special skill such as speaking the local language. Or they may act as nurse or even security guard (particularly in the case of a female business owner travelling to a developing country).
Perhaps they help you meet the “cultural or social expectations of a foreign host or business contact”. If, say, you were hoping to secure a contract in South America and have been invited to a contact’s home, your host may expect you to take your spouse. Although “ostensibly a social occasion, the contract rides on meeting those expectations”.
Note the difference between an employee and a sole trader or business partner. In the former case you need to show that your spouse’s presence is essential; in the latter case merely that it is desirable (to impress that South American contact).