Roman culture in Britain largely dissapeared after the Saxon migration. You mentioned loanwords; most Latin words in the English language were introduced (reintroduced, in a way) by the Normans, who spoke a French dialect.

In other parts of Europe the ruling Germanic tribes made an effort to preserve some parts of Roman civilization. The Franks for instance had been in contact with Roman culture for centuries and had adopted christianity. The Saxons were still pagan at this point and probably didn't appreciate Roman civilization as much as the Franks or the Goths.

I suppose it's possible that Britain never was as thoroughly romanized (or in general: developed) as Gaul or Hispania, and that Roman culture was less durable because of it. Actually Great Britain has always been sparsely populated compared to other parts of Europe until modern times.