The relevant part quoted by Knighton is book 1, chapter 14, here copied from the Latin Library:

Cessante autem uastatione hostili, tantis frugum copiis insula, quantas nulla retro aetas meminit, affluere coepit; cum quibus et luxuria crescere, et hanc continuo omnium lues scelerum comitari adcelerauit; crudelitas praecipue, et odium ueritatis, amorque mendacii, ita ut, siquis eorum mitior et ueritati aliquatenus propior uideretur, in hunc quasi Brittaniae subuersorem omnium odia telaque sine respectu contorquerentur. Et non solum haec saeculares uiri, sed etiam ipse grex Domini eiusque pastores egerunt; ebrietati, animositati, litigio, contentioni, inuidiae, ceterisque huiusmodi facinoribus sua colla, abiecto leui iugo Christi, subdentes. Interea subito corruptae mentis homines acerba pestis corripuit, quae in breui tantam eius multitudinem strauit, ut ne sepeliendis quidem mortuis uiui sufficerent; sed ne morte quidem suorum, nec timore mortis hi, qui supererant, a morte animae, qua peccando sternebantur, reuocari poterant. Unde non multo post acrior gentem peccatricem ultio diri sceleris secuta est. Initum namque est consilium, quid agendum, ubi quaerendum esset praesidium ad euitandas uel repellendas tam feras tamque creberrimas gentium aquilonalium inruptiones; placuitque omnibus cum suo rege Uurtigerno, utSaxonum gentem de transmarinis partibus in auxilium uocarent; quod Domini nutu dispositum esse constat, ut ueniret contra improbos malum, sicut euidentius rerum exitus probauit.

The Medieval Sourcebook gives as a translation:

When however, the ravages of the enemy at length ceased, the island began to abound with such plenty of grain as had never been known in any age before; with plenty, luxury increased, and this was immediately attended with all sorts of crimes; in particular, cruelty, hatred of truth, and love of falsehood; insomuch, that if any one among them happened to be milder than the rest, and inclined to truth, all the rest abhorred and persecuted him, as if he had been the enemy of his country. Nor were the laity only guilty of these things, but even our Lord's own flock, and his pastors also, addicting themselves to drunkenness, animosity, litigiousness, contention, envy, and other such like crimes, and casting off the light yoke of Christ. In the meantime, on a sudden, a severe plague fell upon that corrupt generation, which soon destroyed such numbers of them, that the living were scarcely sufficient to bury the dead: yet, those that survived, could not be withdrawn from the spiritual death, which their sins had incurred, either by the death of their friends, or the fear of their own. Whereupon, not long after, 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.

Now, to me it looks like Bede is just doing his typical moralising, in parallel to the biblical punishments and the sinful behaviour of the Jewish people under Moses. Interestingly, he does provide a specific date for the events under discussion, in the next sentence: 449 AD.

We can trace the quote further, though. In this section, Bede is simply repeating what he had read in Gildas' De Excidio et Conquestu Britanniae, where the same phrasing is used, I quote from the public domain:

interea uolente deo purgare familiam suam et tanta malorum labe infectam auditu tantum ribulationis emendare, non ignoti rumoris penniger ceu uolatus arrectas omnium penetrat aures iamiamque aduentus ueterum uolentium penitus delere et inhabitare solito more a fine usque ad terminum regionem. nequaquam tamen ob hoc proficiunt, sed comparati iumentis insipientibus strictis, ut dicitur, morsibus rationis frenum offirmantes, per latum diuersorum uitiorum morti procliue ducentem, relicto salutari licet arto itinere, discurrebant uiam.

dum ergo, ut salomon ait, ‘seruus durus non emendatur uerbis’, flagellatur stultus et non sentit, pestifera namque lues feraliter insipienti populo incumbit, quae in breui tantam eius multitudinem remoto mucrone sternit, quantam ne possint uiui humare. sed ne hac quidem emendantur, ut illud esaiae prophetae in eo quoque impleretur dicentis: ‘et uocauit deus ad planctum et ad caluitium et ad cingulum sacci: ecce uitulos occidere et iugulare arietes, ecce manducare et bibere et dicere: manducemus et bibamus, cras enim moriamur’.

appropinquabat siquidem tempus quo eius iniquitates, ut olim amorrhaeorum, complerentur. initur namque consilium quid optimum quidue saluberrimum ad repellendas tam ferales et tam crebras supra dictarum gentium irruptiones praedasque decerni deberet.

tum omnes consiliarii una cum superbo tyranno caecantur, adinuenintes tale praesidium, immo excidium patriae ut ferocissimi illi nefandi nominis saxones deo hominibusque inuisi, quasi in caulas lupi, in insulam ad retundendas aquilonales gentes intromitterentur. quo utique nihil ei usquam perniciosius nihilque amarius factum est. o altissimam sensus calignem! o desperabilem crudamque mentis hebetudinem! quos propensius morte, cum abessent, tremebant, sponte, ut ita dicam, sub unius tecti culmini inuitabant: ‘stulti principes’, ut dictum est, ‘taneos dantes pharaoni consilium insipiens’.

And here Giles' translation on Project Gutenberg:

Meanwhile, God being willing to purify his family who were infected by so deep a stain of woe, and at the hearing only of their calamities to amend them; a vague rumour suddenly as if on wings reaches the ears of all, that their inveterate foes were rapidly approaching to destroy the whole country, and to take possession of it, as of old, from one end to the other. But yet they derived no advantage from this intelligence; for, like frantic beasts, taking the bit of reason between their teeth, they abandoned the safe and narrow road, and rushed forward upon the broad downward path of vice, which leads to death. Whilst, therefore, as Solomon says, the stubborn servant is not cured by words, the fool is scourged and feels it not: a pestilential disease morally affected the foolish people, which, without the sword, cut off so large a number of persons, that the living were not able to bury them. But even this was no warning to them, that in them also might be fulfilled the words of Isaiah the prophet, "And God hath called his people to lamentation, to baldness, and to the girdle of sackcloth; behold they begin to kill calves, and to slay rams, to eat, to drink, and to say, 'We will eat and drink, for to-morrow we shall die.'" For the time was approaching, when all their iniquities, as formerly those of the Amorrhaeans, should be fulfilled. For a council was called to settle what was best and most expedient to be done, in order to repel such frequent and fatal irruptions and plunderings of the above-named nations.

Then all the councillors, together with that proud tyrant Gurthrigern [Vortigern], the British king, were so blinded, that, as a protection to their country, they sealed its doom by inviting in among them like wolves into the sheep-fold), the fierce and impious Saxons, a race hateful both to God and men, to repel the invasions of the northern nations. Nothing was ever so pernicious to our country, nothing was ever so unlucky. What palpable darkness must have enveloped their minds-darkness desperate and cruel! Those very people whom, when absent, they dreaded more than death itself, were invited to reside, as one may say, under the selfsame roof. Foolish are the princes, as it is said, of Thafneos, giving counsel to unwise Pharaoh.

Gildas, being a preacher, is a bit more explicit in his biblical references. However, he is also writing at a time when plague and famine were a real thing. Gildas wrote history not for history's sake, but as a lesson and warning to his contemporaries. To Gildas, all the hardships of the Britons are due to their vices. His text is thus a warning to his contemporaries, and the calamities he describes might more reflect the time he is writing in than the time he describes. The common date for Gildas is somewhere in the early 6th century, which fits very well with an actual famine and plague we do know of: the plague of Justinian in 541-542. We know that the plague, which devastated the Eastern Mediterranean, would likely have had an increased impact in Northern Europe, which would have recently suffered from the year without summer of 535-536. The effect of the plague might have been slightly delayed in northern Europe, where the Welsh Annals record a 'mortalitas magnas' for 547 AD (year 103 in the Welsh system), while the Annals of Ulster record it for 548 AD (year 549 in the Irish record).