As a Briton myself that completely enrages me.

Corbyn was accused of being an anti-semite because some unidentified people in Labour, people who weren't directly associated with Corbyn, allegedly said some anti-semitic things, things whose details we never heard, and that Corbyn was unable to stop these unnamed people from saying whatever it is they said.

For this, the Simon Wiesenthal Center named Corbyn "anti-semite of the year", ahead of an American man who after posting anti-semitic hatespeech online, went into a synagogue with semi-automatic weapons, killed 11 and injured 6.