I assume he surely knew about its existence. There were many Baalei Tosfos that lived in England. e.g. רבינו יעקב מאורליינש, משה בן רבינו יום טוב מלונדריש רבינו, there is a chibur named תוספות חכמי אנגליה.
According to some, the אבן עזרא is buried in England or at least visited England at some point. If the Ibn Ezra who came from Spain was able to travel to England, I’m sure Rashi who lived in France had at least knowledge…