This really sucks. Is it just an estimate and am i likely to get 80mbps? £31 a month for 45 - 50 mbps would really suck!
You're likely to get what it predicts.
The predictions come from a model which takes into account the type and length of your line, i.e. the loop distance from the cabinet to your property. It can also take into account previously-seen speeds on FTTC at that particular property.
You *might* get a bit faster, but you could just as well get slower.
45-50Mbps is not a bad speed. I used to get 25-30Mbps on FTTC (and 4Mbps upload).
You can get a rough idea of FTTC speed based on line length from the cabinet here:
https://www.increasebroadbandspeed.co.uk/chart-of-bt...
As people have migrating from ADSL to FTTC, speeds have also been reducing due to crosstalk:
https://www.increasebroadbandspeed.co.uk/2014/vector...
Openreach chose not to pay to turn on vectoring except in a few limited areas.