Gaulish tribal etymology?

From: Michael Smith
Message: 29064
Date: 2004-01-04

Hi, I came across this from Will Durant (long ago, I know):
 
"When Caesar came he found the island  peopled by several independant tribes, each with its expansive king.  He gave to all the population the name Britanni, from a Gallic tribe, so called, just south of the Channel, in the belief that the same tribe inhabited both shores."
 
Thoughts?  Is there any truth to it?
 
-Michael