Because King William believed he was the rightful successor to Edward the Confessor, his first written statements and proclamations were made in English, just like the kings before him. After a period of rebellion between 1068-1070, William began to rely less on the English for support and more on his close Norman advisors. It is only after 1070 that Norman culture becomes dominant at the top of English society.
Most of the information historians have about England during this time teaches us about what life was like for the wealthy and educated. In these sources it is clear that French was becoming the main language used at court and in government.
Justice, prison, constable, agreement, fine, court, debt and evidence are all words that were introduced into the English legal system by the Normans. Although Anglo-Saxon England had a sophisticated legal system, the Normans began to introduce aspects of the French system that they were familiar with after 1070.
Most of these changes were gradual and were not hugely different from Anglo-Saxon times. The key difference was the introduction of a law designed to protect the outnumbered Normans against Anglo-Saxon attacks. This law was called murdrum - it forced the Anglo-Saxon villagers to prove that any corpse found near their village was not a Norman. If it was a Norman then the whole village was responsible for finding the culprit and had to pay a heavy fine after the murderer was executed.