A key player in the European Parliament has told Boris Johnson that he is talking nonsense by criticising pro-Europeans in the UK for having split allegiances.
Guy Verhofstadt, the Brexit co-ordinator for MEPs, told Irish politicians that the Foreign Secretary's attitude was out of date.
In a special address in the Dail parliament in Dublin, the former Belgian prime minister also repeated his insistence there can be no return to a hard border of checkpoints on the island of Ireland in the wake of Brexit.
"I note that some British politicians, not to name BorisJohnson, criticise their countrymen and women for wanting to keep their European identity," he said.
"He accused them even of split allegiance.
"I think that is a binary, old fashioned and reductionist understanding of identity.
"I think we need to be smarter, and more open and more inventive than that."
Mr Verhofstadt launched the broadside at Mr Johnson's weekend newspaper article on Brexit as he addressed politicians who sit on the Irish parliament's committees on European Affairs, Foreign Affairs and Trade and Defence, and the Good Friday Agreement, saying that people can identify however they choose.
"It's not your origin or the fact that by accident that you were born in this or that village, city or country that makes you a good citizen. No, it's the fact that you embrace the values of your community," Mr Verhofstadt said.
"I think it's nonsense to talk about split allegiance.
"It's perfectly possible, I think - I never practice it - but to feel English, British and European at the same time.
"And I think it is perfectly normal to be a Dubliner, Irish and European ... without being schizophrenic about split allegiance.
"It is this position that needs to be defended by our European Union just as the European Union needs to defend there is no return to the past, to hard borders on our continent, and certainly not to a hard border between Northern Ireland and the Irish Republic."
The Brexit chief negotiator, Michel Barnier, was the last dignitary given the same opportunity to address Irish politicians.
Mr Verhofstadt reiterated that the onus is on the UK to come up with a workable solution to the Irish border question.
On Wednesday he was in Belfast meeting politicians and later visited a border farm in Co Monaghan, remarking how it is impossible to see where one jurisdiction starts and the other ends.
Mr Verhofstadt described the Irish border as an "illogical divide" and called for it to remain invisible.
"Certainly the cows couldn't see it. Cows from the north eating grass from the south, milked in the north by a farmer from the south with their milk bottled in the south," he said.
"I'm a Belgian so surrealism comes naturally to me but to reinstate the border would be more than surreal, it would be totally absurd, even for me."
While criticising Mr Johnson's article where he raised concerns that EU membership gave Britons a competing loyalty, Mr Verhofstadt told politicians that in the past the Irish border created "hate and chaos".
He said everyone he met on his trip to Belfast and the border region told him they wanted Northern Ireland to stay in the customs union and single market.
"This can only be a unique solution," he said.
"Simply saying that the problem will be solved by using new technology is in my opinion not convincing."