Denied Vodafone Gigafast speeds that BT already provide to my address?

[dg1987]

I want nothing more than to become a Vodafone Gigafast customer, particularly at the Black Friday prices recently offered in the Vodafone leaflet posted through my letterbox which said I could have up to 900mbps speeds. However Vodafone's call centre said the system could only offer me 100mbps, this is despite my property being on FTTP with BT for many years, and my current speed is 300mbps (BT will provide me 900mbps if I wished). Is there any reason Vodafone can offer FTTP at 100mbps to my property, but no higher, when other providers can? Am I trapped with BT at 50% higher prices if I wish to maintain 300mbps or more? (yes I realise first world problem compared to most broadband speeds!)

Thanks,

Dan