Way back into the first millenium, which is only practically achievable by connecting to royalty (which we are all likely to be descended from somehow - I'm certainly nothing special).
Parish records back through various framework knitters, weavers, husbandmen etc to Robert Heathcote, the son of cobbler, who was born 1675.
He married the youngest daughter (and orphan), of a local minor landowner Raphael Bradbury. This mismatch almost certainly achieved because a relation of his stepfather mas married to her elder sister, whom she lived with after her parents' deaths.
Combination of parish records and wills back to Raphael's gr gr grandfather George, born c1518, who married Anne Gilbert.
Herald's visitation, supported by a deeds, church monuments etc back to her great grandfather Robert, born before 1450
Church monument and herald's visitation to his father in law John Statham, born circa 1405.
Dispute over inheritence at TNA to his maternal grandfather Richard Cornwall, and then IPMs, supported by copious entries in the rolls (close, patent, fine etc) back to his gr gr gr grandfather Richard earl of Cornwall, second son of King John.
Then once you hit royalty, you can't fail but get back to pre-conquest times - just how far back you claim depends on how much you believe certain ancient documents - for example king Alfred's biography, written contemporary to his reign (I can't just remember the name of the chronicler off the top of my head) gives Alfred's lineage, but how many generations you trust it for is debatable - it claims to give it all the way back to Adam and Eve !
