There was a time that the Frisians attacked England once in a while. When attacking they took all kinds of goods, like a viking-raid. After some years the Frisians decided to set up some settlements in England. Many of these settlements survived till today and that’s why England has many places with Frisians roots and names. Down here you’ll find a list of some Frisian places in England (the list is not complete)
By that said you can also make the conclusion that a part of the English population has Frisian blood.