and they probably paid maybe £20k installation. Rental costs ... maybe £500 per month.
Sounds about right.
We were paying around £7,500 pa rental costs on a 2Mbps (up & down) fibre connection (and it's gone up since we upgraded it to 10/10).
Rarrar; as has been mentioned, whilst this is a fibre to the premises, it is not FTTP (or at least, not the FTTP that's being trialled by BT in some favoured areas). It's the old, expensive way of getting a fibre connection (you may have heard of "leased lines", "Ethernet over fibre", etc.).
Expect it to be expensive and nowhere near the speed you might think.
Whilst anything up to around 10Gbps is available over such a connection, the prices are so high most businesses opt for much lower speeds (10Mbps is typical).
ADSL2+ with BE
DL Sync around 4.8Mbps
UL Sync 1088kbps
DG834GT with DGTeam firmware