In his conference speech Millar attacked Plaid Cymru and Reform, who polls suggest are vying to win the Senedd election.
“Plaid want people to think they are a bunch of friendly moderates, but they are nothing of the sort. They are extremists,” he said.
He said a Plaid government “would focus their time, energy and attention on their ultimate aim, to rip Wales apart from the rest of the UK.
“Independence would jeopardise people’s pensions, and ability to live, work, or study in other parts of the United Kingdom.”
Plaid Cymru has said it would not try to hold a referendum on independence in a first term of a Plaid government, should it win the election.
Millar said Reform “love to wag their fingers and identify problems, but they offer no credible solutions whatsoever”.
“They don’t want to be in government next May after those elections to the Senedd,” he will say.
“Nigel Farage himself has openly acknowledged that his party is not ready to govern. He has simply said that his aim is that he wants Reform to be the largest opposition party.”
“Reform is not a serious party. They are a limited company more interested in selling football shirts and merchandise at events, than running a country.”
Millar also described Wales as “broken” after 27 years of Welsh Labour government rule, with failing education and health systems.
“Labour has absolutely no solutions to these problems. They have failed our schools. Failed our NHS and failed our economy,” he will say.
“Wales is the sick man of Britain. It’s not good enough.”