In reply to a post by MrSaffron:

Looked at a few premises with no full fibre or Virgin Media options and Rightmove is suggesting 900Mb

Oddly they do seem to get speed estimate better in the one place I checked where full is available.

It reverts to a simple hard earned truth ….

Never trust an estate agent.

Try CO13 0QX

FTTC area and while lightspeed nearby they are not on the road or next door road

Ultrafast

900Mb

Average download speed of the fastest package at this postcode*

is what they say, but for Recommended Deals they show FTTC packages correctly.
My guess is they use a wider area than postcode let alone actual address

Buyer beware.

Many things are not checked by a surveyor when buying a property. Why should agents be any different.