Sky News reported that Davies, in reference to the Israeli-Palestinian conflict, wrote in an e-mail message that Jews, despite experiencing the Holocaust, had "themselves become oppressors."
When the constituent protested, the Jewish News quoted Davies saying in his reply, "Sounds like racism to me. I hope you enjoying wallowing in your own filth."
In a statement, Davies said: "I apologize for the language and tone of my e-mail, which was unacceptable and without justification. I should never have used the words I did in the e-mail," Sky News said.
The Telegraph reported that the party has distanced itself from Davies' remarks.
Davies will stay an MEP, but his leadership post is expected to be taken over by Sarah Ludford.