Upgrading to Fibre with no Master Socket

[#1]

Hi - apologies if this is discussed elsewhere.
I've been with PlusNet for donkeys years and have a 2740N router plugged in to a micro filtered extension socket chugging away nicely. I do not have a BT master socket as such, my phone line comes in to my attic and is joined to a junction box and then joined to the extensions.
Will I be able to upgrade to fibre by plugging my router into the BT fibre modem and then into the extension socket using a filter? I appreciate that this may be detrimental to my speed but it's working ok now.

[#2]

BT Openreach no longer provide a fibre modem as Plusnet provide a combined VDSL Modem/Router (Plusnet Hub One).
If you ask for a self install fibre upgrade then you will be able to plug in the new Plusnet Hub One modem/router into any extension socket using a filter.

[#3]

Quote from: acr

If you ask for a self install fibre upgrade then you will be able to plug in the new Plusnet Hub One modem/router into any extension socket using a filter.

Anyone know how you ask for self-install?  It's not something I saw when going most of the way through the process to change product.  It just suggests a bunch of time slots for the engineer visit.
cheers
Andy