Lib Dem MEP Chris Davies has resigned as the party's leader in Europe over comments to a Jewish constituent.
Chris Davies was involved in row with constituent
North West England MEP Mr Davies told an e-mail correspondent he hoped she enjoyed "wallowing in her own filth".
She had written to Mr Davies to disagree with comments he made about Israeli policy over Palestine.
He had said it was difficult to understand why those whose history was of oppression "did not care that they themselves had become oppressors".
The constituent wrote to Mr Davies: "You make the same mistake as many others who call themselves liberals.
"You seem to equate the situation of the Palestinian people as being exactly the same as the Jewish victims of the Holocaust."
The Jewish News reported that Mr Davies responded in an email: "Sounds like racism to me. I hope you enjoying wallowing in your own filth."
Mr Davies, who initially apologised for the remarks, has now resigned as Liberal Democrat European leader but will remain an MEP.
In a statement Mr Davies said: "I apologise for the language and tone of my email, which was unacceptable and without justification.
"I should never have used the words I did in the email. I have written to the lady concerned, apologising."
Party leader Sir Menzies Campbell commented: "Chris Davies has rightly made a full apology for his remarks.
"I discussed this matter with him today, when we agreed that the proper course for him now is to resign as leader of the Liberal Democrat MEPs.
"What he said was unacceptable and he recognises that unreservedly.
"Chris Davies has made a very considerable contribution to our Party over a long period and I am sorry that it has become necessary for him to resign his leadership. I deeply regret the offence his remarks have caused to the Jewish community."