Get an accountant. Save lots of money. Or, don't bother, and ask window cleaners instead.
+1
Remember, every expense you claim for has to be justifiable- fish & their tanks in a self employed window cleaners home office is not. Don't forget, it will be you who will have to prove every penny & every percentage breakdown of every claim should they require you to do so with the possibility of backdating the scrutiny of your entire accounts for the last 6 years!
Best way to claim IMO is "use of home as office". A reasonable amount which will cover your office space & laundry expenses subject to inflation year on year. Doesn't have to be exact, just there abouts, reasonable.