The Norman invasion into England in the year 1066 put an end to the Anglo-Saxon language (which was considered peasant jargon), the Normans speaking Latin and Gentry French.
The Anglo-Saxon masses did not totally abandon their English language, however. Manorial servants, merchants and monks also kept the language alive, and by the mid 13th century written and spoken English began a revival. While the Provisions of Oxford (1258) was written in French and Latin, the copies sent to the shire courts were in English. Hostilities with France led to a rise in nationalism and the defense and resurgence of the English language.
The London city council conducted business in English, and in 1362 a London petition led to a statute passed that proceedings in their courts would be conducted in English. University students and monks spoke English rather that Latin and French, and by the mid 14th century middle and upper classes were also speaking English.
The plague also had a part in the revival of spoken English. When the Black Death led to the demise of the church leaders who spoke French and Latin, the English-speaking lower classes replaced them. As the years went by, the peons experienced such things as freedom, prosperity, and political clout, taking with them to higher places their language.
While the English language was expressed orally during these centuries, the written word was still recorded in French and Latin (but sometimes in English).