With Plusnet you still get the original type of two-box installation, not a combined modem/router. If you are happy for the modem (needing a power socket) to be close to the master socket, then you would need to buy a suitable length of Ethernet cable to connect it to the router wherever you want that, (Up to 100 cable-metres).
If you want the modem to be where you want the router you have to order the "Data Extension Cable", (also called the "Home Wiring Solution"). It's free but Plusnet do not order it unless requested. I believe that if you order online it is an option during the process.
This allows a data socket for the modem to be located where you want it. The standard maximum length is 30 metres. Theoretically it could be longer but initially there was a standard cable of that length, that Openreach carried for such orders.
It is also possible for an exterior grade cable to be used as a data extension cable if you and the engineer agree that is sensible and practicable. If you get a subcontractor such as Kelly's or Quinn's I wouldn't rate your chances of that.