Between Gildas, writing around 550 AD, and the Anglo-Saxons, beginning their writing around 850 AD, was another cleric named Bede. Bede's Ecclesiastical History of the English Nation is considered by most to be the first true history of the English Nation. He was born in 673 AD and ordained deacon in 692 AD. He was made a priest in 703 AD and died 735 AD. He wrote his account around 700 AD. He is brought up in an Anglo-Saxon world, that had become Christians since Gildas called them "...a race hateful both to God and men...".
In Chapter XIV of his book, Bede writes the following: "...Whereupon, not long after, [a severe plague is described], a more severe vengeance, for their horrid wickedness, fell upon the sinful nation. They consulted what was to be done, and where they should seek assistance to prevent or repel the cruel and frequent incursions of the northern nations; and they all agreed with their King Vortigern to call over to their aid, from the parts beyond the sea, the Saxon nation; which, as the event still more evidently showed, appears to have been done by the appointment of our Lord Himself, that evil might fall upon them for their wicked deeds."
Here is recorded that "...they all agreed.." to invite the Saxons over for a visit. Thus grandfather Vortigern had help in his decision. Bede also feels that God himself arranged the whole thing so that the Britons would be punished for such evil ways. It certainly seems to make a difference as to who is writing the checks!
Bede's writings are found in "Bede's Ecclesiastical History of The English Nation", J.M. Dent & Sons, Ltd., London, 1910. The quote above can be found on pages 21-22.