Luxembourg is growing faster though. So at one point it did have less inhabitants than malta. But not since about 1950
It would be better to word the question as 'Germanic tribe that invaded Britain after the Romans' or put the approximate time period.
"A 2016 study concluded that on average 25–40% of the ancestry of modern Britons was contributed by Anglo-Saxon immigrants."
Lots of other sources confirm this. The Romans, on the other hand, did not leave much of a genetic trace.