What if the Romano-British version of Vulgar Latin survived? Different Ango-Saxon Invasions

So essentially minimizing the influence of the Anglo-Saxon-Jutes on Britain, and keeping them either totally out, or having them assimilate into Romano-British culture and language. How would this be possible?

Assuming this version of Vulgar Latin survived into its own Romance language a la French, Spanish, Romanian etc. what would it sound like? Would it have significant Celtic influence? What would the effects of a Romanized Britain be w/ no Anglo-Saxons?
 
What would appears would probably be something like IOTL Breton, rather than a Romance language. In fact, rather than one post-Roman speech, you'd probably end up with a set of various Brythonic dialects which are less influenced by Latin the more you go North.

Britain was fairly untouched by Roman civilisation, compared to other western provinces and while you could have lasting romance features, post-classical Britain wouldn't not have such nearly as the same extent than in Northern Gaul (to say nothing of western mediterranean basin).
Culturally and structurally, it would look like a lot like other non-Gaelic celtic ones. (And from what we know, it already fairly looked like this IOTL after Roman withdrawal, rather than a post-classical romance speech).

That said, you'll have a relatively strong Romance and Latin influence trough imperial superstrate of course, but as well from post-imperial influences such as Gallo-Romance influence or Church Latin (that were the main reason of the latin superstrate in gaelic IOTL). But that would remain a Brythonic language with more or less important Latin, Gaelic and Germanic influence.

What would the effects of a Romanized Britain be w/ no Anglo-Saxons?

First, we have to define what romanisation means.

It can be compared to creolization on this regard : what made a roman society was the law, the roman civic conception both imperial and municipal, and religion (imperial cult and later Christianism). On this regard, most oriental provinces were as much if not more romanized than the average western province, even if latin language wasn't dominant (outside urban centers, it was more a situation of diglossy than monopolist : Gaul was still a living language by the IV/Vth centuries).

People as Ambrosius Aurelianus/Riotomagus (whatever they were the same person, as I think, or not) clearly represented how romanized imperial and post-imperial Britain was, up to still interacting with continental business.

But one of the differences with Britain from one hand, and Gaul or Spain on the other hand is that these two provinces were quite develloped already on their own (Spain beneficing from ancient trade, for exemple; and Gaul being an agricultural and artisanal powerhouse) while Britain was a bit more undevelloped.
Provincial elites were often the same than before the roman conquest, the romanisation fitting right in the shoes of the previous situation.

In Britain, it seems it was far less the case : tribal structures remained largely in place (and survived up to the VIth century). Not that, again, Britain didn't knew a form of romanisation, but it remained largely stuck to the south-eastern part of the province, and more as an urban and coastal feature (which may have played historically : it's possible that the House of Wessex is issued from a mix of Britto-Roman, Saxon established in Southern England since the IIIrd century as federates, and Saxons established since the Vth themselves)
 
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