If you are using one of your rooms within your house as an office, which most people do, then you can also claim a %age of all your household costs against the business.
ie: If you have 7 rooms within your house, then total up all your yearly household bills and claim 1/7th of it against your business.
You can claim for:
Electric, gas, water, council tax, and any other general running costs.
Keep receipts for all your washing powder and claim a percentage of that. £5.00/day would not be an unreasonable amount to claim for daily laundry (wear on machine, powder, electricity, your time)
I would always recommend you get a good accountant, they will save you more than they will cost you, a decent accountant will charge between £100-£250 for a basic set of year end accounts and will advise you on what you can and cannot claim for.