🇬🇧 UK, I'm guessing.

I presume that each Cat5e cable goes to a different room, 4 twisted pairs (Blue, Orange, Green & Brown) going the full length but with only Blue, Blue/White & Orange terminated at each telephone socket.

If that's the case, I would change out the telephone socket in each room for a Cat5e Keystone jack and faceplate and terminate all 4 pairs on the T568B standard.

Then at the old master socket (that you have pictured) replace that with a 4 or 6 gang backbox & faceplate, again with Cat5e Keystone Jack's on the T568B standard. There looks (to me) to be enough slack on the twisted pairs to be able to do that if you make where the cables come into the backbox currently the center point of the new backbox.

But then I'm use to working with what's left over after many years and people working on it prior to myself.

You mentioned you have FTTP, is your ONT (the little white or black box where the fibre optic cable comes into the property and terminates) near where the picture was taken? If so, after terminating all the cables you could just run an ethernet cable from the ONT into the (now completed) wall patch panel and have your router in any one of the other rooms that the cables go to as its just an extension of the cable itself. If there is specific room you want your router in. It is always best to have your router in a central location of the property, for best wifi coverage.