It certainly used to be standard to run 2 pairs between the distribution point and the master socket, but I believe more recent drop cables contain more than 2 pairs.
A few years ago, I was led to believe that standard BT practice for underground feeds was to use 5 pair cable, but I don't know whether this also applied to overhead feeds. Things may well have changed again now that the likelihood of multiple residential lines has reduced - the days of a second line for dial-up Internet access or fax are largely behind us. 2 pair cable is most likely to be 'pair and a spare' these days.
Hopefully someone can give a definitive answer on current BT Openreach practice.
How many fibres are run into a property during an FTTH installation? There's some arguments to run a bundle containing more than one fibre, even if you only fuse one fibre to the beam splitter (BT GEA-FTTH is single fibre PON using beam splitters, not a point-to-point duplex fibre link).
Experience might show that damage to one fibre typically means the entire bundle is unusable, or that it is quicker to replace the fibre to the premises whenever possible rather than try remaining fibres in the same bundle. In either of these cases, there's little point having spare fibres in the bundle.