BT Caller Display now free from Oct 1st. If you are a BT customer and do not have Caller Display, you can now get it for free. It is not automatic if not already included in your package.
To get fee caller display use the link then select manage Landline features. You need to select the option for BT Caller Protect with caller display included. This will generate an order to add it your line at no extra cost.
I followed these steps last night and caller display is already enabled.