You're in Bassett aren't you ? I'm not sure if this applies to the outer suburbs, but on my side of town it's a combination of fibre optic and copper cable.
I don't know if you're aware of the history, but it's here:
https://en.wikipedia.org/wiki/Swindon_Cable
In a nutshell, in Swindon, Virgin Media broadband uses some of the old Swindon Cable TV network.
My Virgin Media fast fibre broadband was
technically mis-sold to me as 'fibre broadband right to your door'.
It's fibre broadband to the green junction box at the end of our street (about 100 yards away). From there it's copper cable to the house.
When they first installed mine, they couldn't reach the contracted 100 MB/s speed (let alone the 'super fast' 200 MB/s option).
Initially I was getting only 22 or 23 MB/s, so they had to run a new cable. That's when I found out it was actually copper.
Incidentally, Virgin Media's fibre distribution hub / control centre is the old Radio Rentals / Swindon Cable building on the Hawksworth Industrial Estate - corner of Newcombe Drive and James Watt Close.