I gather this problem is peculiar to computer users in the UK or anyone wanting to use the Pound currency symbol. I normally have no need to use the Pound currency symbol but, if I did, it would probably be in Microsoft Excel and, if I recall correctly, I have used it in Excel.
Anyway, I find your post a little confusing, so, in case other viewers might also find it confusing, perhaps some clarification is needed. You are talking about the key that shows number 3 and #, right? And, do you want that key to type # or the Pound currency symbol, when the Shift key is held down?