Conservative MP Daniel Kawczynski has been reprimanded by his party for sharing a platform with some of Europe's leading far-right politicians.
The party said his appearance at the same event as Hungary's nationalist PM Viktor Orban and Italy's ex-deputy PM Matteo Salvini was "not acceptable".
The Conservative Party said the MP had accepted this and apologised.
Labour and Jewish campaign groups have been calling for him to be suspended from the party.
In a statement, the Conservative Party said: "Daniel Kawczynski has been formally warned that his attendance at this event was not acceptable, particularly in light of the views of some of those in attendance, which we utterly condemn, and that he is expected to hold himself to higher standards.
"Daniel has accepted this and apologised."
Mr Kawczynski was among 22 speakers at the National Conservatism event, which took place in Rome earlier this week.
Other participants include Marion Marechal, the niece of Front National president Marine Le Pen, and representatives of Poland's Law and Justice Party and Spain's Vox Party.
On Monday, the MP for Shrewsbury and Atcham defended his participation, saying he would be making the case for nation states against European federalism.
"Orban and Salvini are not to everyone's tastes, of course," he said in article for The Spectator.
"And I don't agree with each and every one of their policies. But I am not Hungarian or Italian and both leaders have been elected on huge popular mandates in their countries. They represent serious ideas and concerns, some of which are shared by people in Britain."
Mr Kawczynski, whose attendance was first reported by the Guardian, added: "Perhaps those criticising the event should take a more inquisitive approach rather than simply attacking its existence and maligning elected politicians from other countries who are due to speak.
"If so, they might discover why the vast majority of Europeans feel more loyalty to their own countries than the abstract idea of a federal European super-state."
But Labour's Andrew Gwynne said that by not suspending Mr Kawczynski, the Conservatives "are condoning his decision to stand shoulder to shoulder with fascists and legitimising the Islamophobia, anti-Semitism and homophobia they promote".
Leading Jewish groups, such as the Board of British Deputies and the Jewish Labour Movement, have also been calling for him to be disciplined.
And fellow Conservative MP Andrew Percy said his colleague's behaviour was "wholly inappropriate", telling the BBC that he had advised him against attending the event.
Correction 20th February 2020: An earlier version of this article described Matteo Salvini as Italy's leader and this has been amended to clarify that he is the former Deputy Prime Minister.