Constantine through to Alfred the Great, William the Conquerer and beyond, Latin would have been spoken by some in Britain for approximately 1500 years.
It is worth noting that words which contain Latin roots are more often than not still Latin and not English. For example, struct is the Latin root of construction and the root has no meaning in English. This is useful to know as the Latin layer of the English code can be treated differently the English layer, when it comes to spelling.
The above represents a very brief and simplistic version of how English spelling system came to be so complex. It is a cocktail of other languages that through time have mixed together thorough political, cultural and social causes to produce what we have right now.
It would however, be remiss of me to not briefly mention the attempt to standardise the spelling of words by Samuel Johnson in 1755, after this great cocktail had been produced. However, there in lies part of the issue. Johnson attempted to standardise the spelling of words and not the sounds that make up those words. Had Johnson standardised the spelling at the phonemic (sound) level, then it is possible that the spelling <ee> could have just stood for the sound /ee/ as in ‘see’. The failure to do this is yet another reason why the English code continues to be so complex.
1 McGuinness, D., 2006. Early reading instruction: What science really tells us about how to teach reading. MIT Press.
2 Anthony, D. 2010. The Horse, the Wheel, and Language: How Bronze-Age Riders from the Eurasian Steppes Shaped the Modern World. Princeton: Princeton University Press.
3 For an in-depth look at the history of the word ‘father’ and to trace it back through various languages, I highly recommend the History of English Podcast with Kevin Stroud.