The country's most prominent anti-vaccination activist is claiming to be an expert witness in a family legal brawl over whether their children should be immunised.

Judy Wilyman, a militant vaccination critic, has lodged an expert witness statement in a Federal Circuit Court matter, which claims the federal government is suppressing evidence immunisation is ineffective and harmful.

Judy Wilyman claims the government is coercing parents and doctors can't prove vaccines are not harmful.

Dr Wilyman has provided the statement in support of a mother who does not want her children vaccinated. The father, who does want his children immunised, has drafted in the former director of the National Centre for Immunisation Research, Peter McIntyre, to provide the court with his appraisal of Dr Wilyman’s claims.

Fairfax Media has chosen not to disclose the details of the family who are party to the dispute, heard before the Federal Circuit Court in Brisbane earlier this year.