It has always been obvious that the line belongs to BT. I pay the quarterly line rental charge.
However, I defy you to tell me what BT's cost price is. Or how you can qualify what Pipex get it for. They wouldn't say - and BT having been screwing their customers for years.
Pipex are nearly £5 a month cheaper than BT. Pipex have also been in business for a lot of years.