With the introduction of Latin and the Roman script, they were even making headway on establishing "English" (what we know as Old English and barely recognizable as being the same language we speak today) in the written form, when the Normans invaded in 1066. That was nearly the death knell of English as French became the official language of the land. It did die out as a written language because of the Norman invasion, but while English absorbed some words we now take for granted (justice, court, and castle) it lived on as the spoken language of the majority of the population. Ironically enough it wasn't until the new "French" empire invaded and conquered Normandy, cutting off all links between the rulers of England and their former homeland, that English made its comeback.
Of course it doesn't take too long for the English to go on the offensive once they've got their own house in order. After taking care of the whole matter of the Catholic church and establishing the Church of England under Henry VIII thus ensuring masses are held in English, not in Latin, their eyes turned further afield. The Puritans took English with them to North America where they incorporated mispronounced Native American words into their vocabulary in taking the first steps in establishing "American English". Then came the first forays into India and the Caribbean.
While initially British merchants in India were forced to learn the language of the rulers as they were dealing with a civilization both older and more sophisticated than their own, eventually the roles were reversed. Taking on the "white man's burden" of elevating the poor misguided coloured people of the world, the East Indian Trading company passed laws prohibiting the teaching of any language but English to those Indians receiving an education. While this was an incredibly patronizing attitude, it did result in the development of "Indian English", which in turn helped support Indian nationalism by supplying those struggling for home rule the vocabulary with which to articulate their demands.
Bragg doesn't mince any words in his descriptions of how English was spread throughout the world. While his conversational approach to delivering the material may sound like he's making light of the way events took place in India and other locales, he doesn't shy away from telling the truth when it comes to showing English being spread by the sword. From Australia to America settlers and traders were backed up with gunships and muskets to ensure that business was carried on in the Queen's English. When the sun began to set on the British Empire after the World Wars of the twentieth century, the American Empire took up the task of imposing the language on the rest of the world through a mixture of economic and martial might. When you think about it, not much has changed since the Germanic tribes left the Friesian Islands.