None of the immigrations into Britain were done by genociding the indigenous population.
Agreed. It was mostly peaceful migrations throughout the history is this island. With the exception of the Norman invasion anyway.
The majority of ancestors for anyone from Britain would mostly be peoples that had been on the island for a very long time. It was mainly the ruling classes that were replaced.
Whilst this is true for the Norman invasion it most certainly isn't true for the Germanic migration of the peoples simplistically known as the Anglo-Saxons. At least a third of English DNA is Anglo-Saxon. Much of that third is likely concentrated in the southeast of England with it diluting the father north and west you go. British place names (as in names derived form the original Celtic language of which Welsh is a descendant of) where almostly completely replaced with English (a Germanic language) names in the east. The vast majority of Germanic immigrants were lowly folk who quickly got to intermarrying with native Britons (or romano-britons at least, the "true" native culture if such a thing could be said to exist had been pushed north and west by the Empire) and began spreading their culture. Probably the most striking example of this (because it's the thing we tend to know most about ancient cultures) is the change in burial traditions.
I don't see why the amount of 'foreign ' blood would be any higher on an island with multiple invasions than it would be in countries with multiple land borders and equally long histories of invasion and redrawing of boarders not to mention natural intermingling of people that were living closer to the border than to the nearest city.
It isn't higher necessarily. I'm no historian, and my slightly-more-than-layman's level of knowledge only extends to this little island I live on really, but afaik a similar history of continual migration can be found anywhere.
It always strikes me as a bit odd that some people seem to want to destroy the idea that English people exist. Btw I'm not English so I don't have any need to defend them. Most countries are a mix and that's probably a good thing.
Who's trying to destroy the idea that English people don't exist? I just like to remind them occasionally that they're a lot closer to their German cousins as most would like to admit. (: