The pro-Brexit campaign group also deleted the offending material, which was posted in response to reports on Wednesday that the German chancellor had made clear a Brexit deal was now “overwhelmingly unlikely” and insisted Northern Ireland remain in the customs union.
Tweeting a picture of the post, Morgan described it as “horrible”, adding: “You don’t speak for Britain.”
In a second tweet that tagged the group’s founder, Arron Banks, he said “it merely serves to confirm the very worst stereo-typical [sic] impression of Leave voters”.
Andy Wigmore, a close friend of Banks who has worked on the Leave.EU campaign, fought back against Morgan, tweeting a picture of a Daily Mirror front page from 1996 when Morgan was editor of the tabloid, that also mocked Germany.
Morgan defended himself by pointing out the paper apologised in 1996, adding: “Your meme isn’t meant as a joke, is grotesquely offensive, and makes you guys look like racist idiots.”
Early on Wednesday morning, Banks himself intervened and said the post “went too far”, although adding: “The real outrage is the German suggestion that Northern Ireland be separated from the UK.”
Banks then said the post would be deleted and “on reflection the point could have been made better”.
The publication of Merkel’s comments, made during a private call with Boris Johnson but released in a series of No.10 briefings on Tuesday, sparked fury in Brussels.
No.10 sources claimed Merkel had told the PM that Britain could not leave the EU unless it was prepared to leave Northern Ireland behind in a permanent customs union.
European Council President Donald Tusk accused Johnson of engaging in a “stupid blame game” ahead of next week’s crucial EU summit.
“At stake is the future of Europe and the UK as well as the security and interests of our people,” he tweeted.
“You don’t want a deal, you don’t want an extension, you don’t want to revoke, quo vadis (where are you going)?”