The correct picture is that if an asset is used part of the time exclusively for a business purpose (childminding), and the cost of maintaining that asset is an allowable expense, then you can claim a fair proportion of that cost. Similarly, if the asset is classified as Plant and Machinery, you can claim a fair proportion of any available Capital Allowances (which for everything except cars is Annual Investment Allowance).
Examples of expenses 'you would incur anyway' but are frequently claimed on a proportional basis are: Council Tax, home insurance, telephone/broadband/mobile phone line rental/inclusive packages, mortgage interest, TV license, satellite/cable TV rental etc.
So the part of Ayla's post I would agree with is "it depends on the circumstances"; this is a subjective judgement of course, and HMRC may view the situation differently than you do. There are three alternatives in this situation:
- Contact HMRC and ask for a ruling. They should give this in writing, and (provided you give them all relevant facts) they cannot change their mind later and charge you additional tax.
- Use your interpretation of the available information to decide whether any proportion of the expense is exclusively for a business purpose and if so, what that proportion is. Include the amount in your expenses, and explain the situation in the 'notes' section of your tax return (e.g. "Allowable expenses include £594 for drain clearance, being 75% of the total cost of £792 incurred. Private usage of the drains is estimated at 25%."). HMRC can challenge this and disallow or reduce the claim, but they only have 12 months from the date you file your return to do so.
- As above but don't include any information on your return. If you are inspected, HMRC can challenge it and disallow or reduce the claim, and if they decide that the claim is fraudulent (i.e. you have deliberately set out to pay less tax than the law says you must) or negligent (i.e. you haven't bothered to think the claim through and come to a reasonable decision based on the available information), they may add a penalty. HMRC have five years from the latest date for filing the return (so for an expense in 2011/12, until 31 January 2018) to investigate.
You might consider taking professional advice from an accountant to help you decide, but note that if HMRC don't agree with what the accountant says the tax bill is still yours - you have no come-back against the accountant (unless the advice they gave was negligent and you incurred additional cost e.g. a penalty as a result).