Alex Richards
Donor
You can't say it was all at once, as there was no unified England yet. Conversion of the general populace had been attempted by the Irish, but generally failed. Conversion really began around 600 a.d.. The last pagan king died in 687. But even then, a lot of the population was still pagan for centuries after, whereas almost all the Franks and their subjects were converted by 800.
Let's be honest, it's not like any of the Lithuanians, Russians, or Magyars were really anything but some tribes until just before Christianization, and while they did convert quite a bit later in some cases, I was speaking more of western Europe. The reconquista was exactly that, a re-conquering I don't think that counts as conversion as they were christian before and during, for some, Muslin reign.
If the Reconquista counts as a reconquering than so do the Augustine missions seeing as the native Britons had already by and large converted to Christianity, we have evidence of some isolated Christian practices through the period as well. Indeed we have examples of 5th Century cemeteries with Christian style Romano-British and pagan style Anglo-Saxon burials in the same area. Frankly your last sentence seems rather like moving the goalposts.
And if we use burial practices as a measure of Christianisation then the population was pretty thoroughly converted by the 8th Century- grave goods decline massively and position becomes standardised on an East-West axis. The main difference is that Anglo-Saxon cemeteries, pagan or Christian, tended to be set up in isolation and weren't focused on a churchyard- mainly because what didn't happen quickly was the large-scale establishment of rural parish churches as Anglo Saxon Christianity tended to favour monasticism and iterant wandering preachers rather than local vicars, though most of the major settlements had parish churches by this time.