If I bought a second you view box would it work exactly like my original
a. If I bought it from BT
b If I bought it second hand or another supplier
I assume you would want 2 YouView boxes in which case: It depends. If you have any of BT's internet channels (Sports or Entertainment channels) on the main box you would not be able to see these on the second box without subscribing to BT's 'extra box' service.
If you just want the freeview channels on the second box that should be ok.
You should be able to 'move' any internet channels between boxes AFAIK (I don't know if there's a limit as to how often you can do this) without an extra box service but wouldn't be able to see on both boxes at same time.
Thank you for reply, I have since found out that as we do not have infinity our line won't support two you view boxes but I think that means that I could not get BT tv on the second one, only the free view. So will have to wait a couple of years for infinity.