The derivation of the word "law" is Teutonic (Anglo-Saxon) lagu, meaning something which is fixed.
The Common Law has Celtic and Anglo Saxon derivation. See, for example, West Saxon Lage.
The Civil Law, which the Normans brought, is Catholic canon law, derived from the Romans, who got it from the Greeks. First codified in the Code of Justinian.
If you are really interested in learning more about the history of the Common Law, most start with Blackstone:
http://www.yale.edu/lawweb/avalon/blackstone/blacksto.htm
For Civil Law, nothing beats Yiannopoulos (as he would tell you himself):
http://www.amazon.com/gp/product/1579803806/sr=8-4/qid=1155755649/ref=sr_1_4/102-6634800-7464918?ie=UTF8
There wasn't really an "England" under the Angles & Saxons. Welsh or "British" law wasn't incorporated into English law.