Background
When in ca. 100 CE Plutarch wrote a treatise entitled Why are the days named after the planets reckoned in a different order from the actual order?, it can be deduced that
- in Rome the seven-day week had supplanted the eight-day week based on market days,
- it was commonly understood the seven days were named for the classical planets in a geocentric universe, i.e., not directly after the deities after whom they were named, and
- the days were not sequenced in their astronomical order: Saturn, Jupiter, Mars, Sun, Venus, Mercury, Moon.
Plutarch's treatise is no longer extant, but we do know the answer: the order follows the astrological planetary hours. Each day of the week is named for the planet ruling its first hour.
The rest is pure arithmetic. Twenty-four hours ruled by seven planets leaves a remainder of three, so beginning with the day of the Sun, the next day is three planets to the right in the list, the Moon's day, and so on.
When after increased contact with the Roman Empire Germanic tribes adopted and adapted the seven-day week, they remythologized the names into more local deities. Whether this twist on the interpretatio germanica included Sunna, a sun goddess, feminine because the Germanic word for sun is that grammatical gender, or was simply a translation of the Latin cannot be determined. Appparently there was no readily available deity to corresponding to Saturn/Chronos, so his name remained for Saturday.
All this occurred long before West Germanic literacy and can only be inferred from Old Saxon, Old High German, and Old English.
...meanwhile in sixth century Portugal
For its own use, the Latin church had adopted the simple numbers of Genesis 1, except the first day was the Lord's day, Dominica, Monday–Friday bore numbers 2–6, and Saturday was the biblical sabbatum. This would not have been so much a reaction to pagan names as it was to assure a distinctly Christian shape to the week, beginning with the prime celebration of the Lord's Day.
The Eastern Church followed a similar pattern, adding Παρασκευή (Paraskeví) for Friday, the "Day of Preparation" for the Jewish Sabbath, on which Jesus of Nazareth was crucified. This "five numbers and the Bible" scheme is still how Greeks name the days of the week, and it influenced Slavic names as well. (Not all names: Monday, e.g., Slovak pondelok, means literally "day after no work," which should be universally adopted.)
In sixth century Portugal, St. Martin of Braga (ca. 520–580) objected to the daily dose of paganism in secular Latin and Romance languages, insisting that not only the days of the week be renamed according to ecclesiastical nomenclature, but that the planets be renamed as well. In the latter endeavor he failed to convince, but to this day, if you're in Lisbon and want to do something on Tuesday, you do it on "Thirdday": terça-feira.
...and now to seventh century England
Sources written in Old English begin to appear in the seventh century, at roughly the same time as Anglo-Saxon Britain was being christianized. These two cultural phenomena are, of course, connected, with much of Old English literature written under the aegis of the Church. Scholars have struggled for centuries to characterize the belief system, if indeed there was one, of pre-Christian Anglo-Saxons, but place names suggest veneration, if not an organized cult, for Woden, Þunor, Tiw, and Frig, i.e., our Wednesday, Thursday, Tuesday, and Friday deities. There is no extant literature from Anglo-Saxon pagans themselves, and what remnants appear are often blended with folklore. Various early kings even claimed Woden or Thor as original ancestors without any concomitant claim of their divinity.
The absence of such sources — plus a relative wealth of sermons and other occasional works in Old English — does, however, make answering your question easier: while there are sources condemning veneration of trees or watercourses as pagan practices, there were no churchmen demanding that the days of the week be renamed according to the Christian numbering. So the Venerable Bede could muse in the eighth century — without the slightest polemic — about the Germanic and presumed pagan origin of the name for the supreme feast of the Christian liturgical year: Easter.
...and a thousand years later
To find an Anglophone equivalent of Martin of Braga, you have to wait for George Fox and the seventeenth century Quakers, who not only numbered the days of the week to avoid any reference to Germanic paganism, but also the months, especially those named for Roman deities or emperors. One Quaker writer enlivened that polemic in 1751, when England finally relented to switching to that "popish" innovation, the Gregorian calendar. This practice continues today, at least in formal contexts, for some more conservative Quaker groups.
