The head of National Museum Wales has been accused of a "rant against Britishness" over comments he made in a speech at a tourism event.
David Anderson said Britain was not "Great" - and claimed the Brexit vote was "madness".
The Welsh Conservatives say he is a public servant and should remain neutral.
Mr Anderson said in response it was the role of museums to pose challenging questions and encourage debate.
While he has spoken out about controversial issues in the past, this time he went much further.
In a speech about promoting tourism after Brexit, the director general said he never wanted to stand beneath another banner that says 'Britain is Great'.
He called the words a lie - and a notion that contributed to the "collective delusional madness" of Brexit.
Mr Anderson said the whole industry should "cease to peddle falsehoods of British 'greatness'.
"I do not wish, ever again, to stand underneath the 'Britain is Great' banner," he told the conference in London at the end of last month.
"The words are a lie.
"They contributed to the collective delusional madness that is Brexit.
"Our tourism industry... must cease to peddle falsehoods of British 'Greatness'."
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Conservative culture spokeswoman Suzy Davies AM said Mr Anderson had a right to an opinion but should be more sensitive about where he expresses it.
"Rather than bring something positive to the table and how to bring Wales more into that sense of greatness, he took the opportunity to paint Britain as this black, dystopian place that nobody would want to visit."
Mr Anderson would not be interviewed but said in a statement it was the role of museums to pose challenging questions and stimulate debate.
"It was in this context that I put forward the argument at the conference that we urgently need a new and more contemporary definition of Britishness in which Wales' voice is much more strongly heard, and that reflects the diversity of cultures and identities of the nations and regions of the United Kingdom," he said.
Who is David Anderson?
- Born in Belfast
- Aged 65
- Married with three children and a former history teacher
- Appointed director general of National Museum Wales in 2010, joining from the Victoria & Albert Museum in London
- His career includes being head of education at the National Maritime Museum and as co-director of London's first cultural quarter, the Exhibition Road Cultural Group
- Honoured with an OBE for services to museums and education in 1999
- He is also the author of best-selling children's books The Spanish Armada and Mutiny on the Bounty
- He lists his interests as including Celtic literature and music, opera, visual arts and Irish rugby
Mr Anderson has made political interventions in the past.
A public disagreement over reforms to the heritage sector led to what an independent report found was a complete breakdown in the relationship between museum management and the Welsh government last year, though things are said to have improved.
For those who have headed our big cultural institutions, dealing with politicians can be a delicate balancing act.
Andrew Green, former librarian at the National Library of Wales said it was important that heads of national institutions were not party political but also that they were not "robots".
"As far as I can see, David Anderson was contributing to a debate about the extent to which Britishness and the role of Visit Britain in advertising for tourists to come to Wales, how those things work.
"I don't think that's party political but contributing to a debate which is entirely fair".
The Conservatives also said the museum had had its problems with income streams and visitor numbers.
The museum took issue with visitor number figures and said it was on track to break records in 2017-18.