I am 12 months into a 24 month contract with BT for their 80/20 FTTC service.
As soon as FTTP became available, I went online to see upgrade options -- the only speed upgrade option I was shown was the 900Mbps service for £45.77 per month, on a new 24 month contract including two free 'Essential Digital Phones' for the Digital Voice migration. Installation next week.
Interesting, a relative whose minimum contract had finished, now has FTTP available.
Like you, they only one option online to upgrade speed (to 900Mbs) but for £67/month!