Why is Britain afraid of a Jewish kid from Kansas City?

Pam Geller isn't the only American Jew to be denied entry into Britain (Robert Spencer isn't Jewish). In May 2012, a Jewish student from Kansas City named Louis 'Chip' Cantor was denied entry into Britain. No one seems to know why.

He was detained for more than nine hours before being put on a plane
back to the United States. At the time, he was not given a reason for
being denied entry,