What can't I claim as a business expense?

The main things you can't claim are:

• Personal costs such as everyday clothing, even if you wear it for work (unless it's a uniform or protective gear)
• Entertaining clients — HMRC doesn't allow this as a deduction
• Fines and penalties such as parking tickets
• The cost of commuting from home to your regular workplace
• Training that helps you move into a new field rather than improving skills for your current one
• Any mixed-use costs where the personal element can't be separated

If you're unsure whether something qualifies, it's better to ask than to claim it incorrectly.