Try the PDF at the bottom of http://superfast-openreach.co.uk/where-and-when/
It gives a list of exchanges that has the Openreach fibre infrastructure available (either FTTC and/or FTTP, or a different technology) to parts of that exchange area.
If you want a deeper look, then you need to be more specific. There is no publically available "master" file with all the areas (down to cabinet or postcode level) where Openreach fibre infrastructure is available.
However it is possible to find out or point you in the correct direction to find information on a specific postcode/cabinet area on whether the Openreach fibre infrastructure is available or will be deployed (either under BDUK or commercially) to that area.
I'm still ondeering why someone would want to kn oe where it was available and not being concerned that they could not get it.
BTW jac, that link doesn't even recognise my postcode.
I suppose that the answer is that when the roll-out has finished then 90% of the country will be covered plus any BDUK funding which enables those areas that Openreach has considered financially unviable.
As the government is pumping millions into BDUK for the "Non-Commercial" areas wouldn't it be better if Openreach was hived off from the BT Group and became Nationalised again?
At present Openreach is not answerable to the public, it's about time that changed (IMHO).