How do i know if an expense is allowable?

smoove

I've bought a 3g card so i can work at customers houses to show them demonstations of their websites, would this be an allowable expense?

Also, how do the HMRC decide if its an allowable expense according to your business type etc?

fengirl_2

You decide - its your business. You need to include in your book keeping all the expenses incurred in running your business.
Is the 3g card used for you personally? No, it is used in the business, therefore you include it in your books.
Every business is different and its up to the business owner to decide what he uses in his business. The law simply states that an expense must be incurred wholly and exclusively in the earning of the profits - it does not have to be necessary (as is the case in an employment).