It is theft, providing you fulfil the requirement of the deprivation. Theft isn't so rigid as to only be the removal of an item. It is also described as 'taking the virtue an goodness out of an item'. So for example, stealing a bus ticket...even if you later return it to the person in question, it's theft if it has been used and the goodness had gone. Also, think theatre tickets etc. (There was a case of London Underground tickets being classed as stolen in this way) Theft is so wide that even if you 'borrow' some money from an employer and don't tell them but do intend to repay it, this too is theft...you must return the exact SAME note itself (R v Velumyl '89)