Bitch means female dog (it's also a word used to negatively describe a woman), so I'm going to guess it's meaning is Female Dog field. Brits are cool.
According to the Wiki page about it is recorded as "Billesfelt" in the Domesday Book.
Could be a Germanic or Norman name, possibly Roman, even old English.
A lot of names of locations from those languages have been changed into similar sounding names over the years, which normally have completely different meanings today.
The town that I live in is called Barnstaple, and you would assume it comes from Barns and/or Stables.
It's actually derived from old English bearde, meaning "battle-axe", and stapol, meaning "pillar". Which comes from a marking of a religious meeting place.
Before that it's from the Roman name "ad Barnastapolitum".
