Broadback writes
Well how do I tell? There are not many of some varieties, so I don't
want to pick and try if I can avoid it, as if it is not ripe that is a
waste.

Place your hand under an apple and gently lift it. If it comes off, it
is ripe.
They don't all ripen at the same time. Varieties are ready for picking
any time between August and late Oct/early Nov, and even on the same
tree, those which get more direct sun ripen earlier.

Lots of windfalls trends to mean the apples on that tree are ready for
picking - the odd windfall is usual, even if the apples aren't yet ripe.

Very late ripening apples need picking in Oct/Nov but will continue to
ripen in store.

Apples will continue to ripen even if picked unripe, but some varieties
(eg Worcester) do not develop full flavour.

If you only have one or two on some trees, you could try putting a net
(eg old stocking) over them, so that if you do leave it too late and
they fall, they land in the net not on the ground, and don't get
damaged.
--
Kay