Self Employed - Working from Home Allowable Expenses

anna2709

Hi
This may be a bit long-winded but I have done lots of research on my question and can't find a definitive answer. Anyway, here goes:
my husband and I are partners in a productions company with another (married) couple, each working from home. We don't use any part of the house "exclusively" for business, but use the garage as a studio (film editing) most of the time and part of the kitchen/living room for the computer, paperwork etc approximately 40 hours a week.
Since the business started (about 3 years ago) we have claimed an allowance for use of home of £5 per week per couple; however the computers are on 12 hours a day (3 of them in each house) which must cost way more than that in electricity, never mind a portion of the usual heating/lighting costs that we wouldn't have if we had an office.
As I said I've done lots of searching on the net for a definitive answer but there doesn't seem to be one - I just want to know how to work out what we should be claiming and if it is worth it!
Thanks - am new to MSE but am addicted already!