He told the JC he witnesses antisemitism when he went to Reubens restaurant with CST Chief Executive David Delew and his wife and witnessed four passersby make comments.
"It was 'Jew this...Jew that' to two members of the community and myself who were just sitting outside having some food and attempting to chat," he said.
"That's the scale of the problem - it's becoming normalised."
Mr Mann's constituency of Bassetlaw had a 5,000 Labour majority at the next election. There will be a byelection to replace Mr Mann unless, as is widely expected, a General Election is called in the coming weeks.
Also in Mrs May's resignation honours is Ehud Sheleg, the Israeli-born co-treasurer of the Conservative Party who donated hundreds of thousands to the party. He receives a knighthood.
