@Cath271 When you refer to the BT box, are you referring to the router?
If you are, then as the router is registered to you and assuming you are keeping BT as your ISP at your new address, then yes, I’m assuming you take it with you because if you don’t and it has to be returned and you leave it at your old address, you’d be charged for non return.
Unless of course you’ve had the router prior to 2019, then I believe you aren’t required to return it.
However, if you mean the ONT (if you have full fibre) then, no, you leave it.
'BT box' can mean anything, you need to be precise with technology.
yes, i have a router. Think i only got this last year.
@Cath271 Then yes, you take the router with you including the power supply lead.