A man who claims to be John Banks' son is taking the former Cabinet minister and mayor to court in a paternity case.

Antony Shaw, now 47, has filed proceedings in the High Court at Auckland asking a judge to declare that Banks is his birth father.

If the case is successful, the former politician could be declared Shaw's next of kin with legal implications relating to potential claims against Banks' will.

The court action follows years of uncertainty around the identity of Shaw's real father.

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Though a DNA test could conclusively eliminate Banks as Shaw's blood relation, people cannot be compelled to provide DNA evidence in paternity cases and Shaw is not seeking any such order from the court.

Shaw, an English language teacher who now lives in Japan with his wife Noriko and son Kent, says the case is not about money. He simply wants certainty about his ancestory for him and his family.

"Mr Shaw has taken this step for no other gain than to have certainty about, and a declaration as to, paternity," his lawyer, Lowndes litigation partner Jacque Lethbridge, told the Herald.

"Mr Shaw wishes to have the details of his biological father recorded on his birth certificate - which details at this stage remain blank - and for his son to know who his paternal grandfather is with certainty."

She added that taking court action against Banks had been a "harrowing and difficult experience" for her client.

"Mr Shaw feels he has been left with no option other than to pursue the matter through the courts."

Lethbridge said her client applied for a legal declaration of paternity against Banks late last year.

However she claimed Banks had not engaged with the proceedings and that it had proved difficult to serve him with documents relating to the case.

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The documents were eventually served on Banks in April and the matter will have its first call in the High Court today.

Banks could not be reached for comment last night.

The former National Party cabinet minister and two-term Auckland mayor was convicted of filing a false electoral return in 2014 in connection with a donation from Kim Dotcom. However he was subsequently acquitted after new evidence came to light.

Banks is married though separated from his wife Amanda. The couple have three adopted children.

Shaw, who has lived in Japan for the last two decades, attended Mt Albert Grammar and grew up believing his mother's Asian partner was his father.

His mother is alleged to have had relationship with Banks in the late 1960s while working as a nurse in Hamilton.

She eventually told Shaw about his parentage in 1999 and he tried to meet Banks in the early 2000s during a trip home from Japan to ask the then mayor "are you my father", a 2001 women's magazine article alleged.

The meeting never happened, culminating in today's court proceedings.

Otago University law professor Mark Henaghan told the Herald paternity cases like this were rare.

They were more usually taken by women under the Family Proceedings Act for child support purposes.

Henaghan said applicants would need to produce strong circumstantial evidence to prove the two parents had been in a relationship at the relevant time, often in the form of sworn affidavits and photographs.

DNA tests could conclusively eliminate someone from paternity. And though a person could not be compelled to take a DNA test, a court could draw "adverse inferences" if they refused.

Establishing paternity was important for some people for identity purposes, and others for their genetic lineage, Henaghan said.

But a paternity declaration also had important legal implications.

"They are your legal father. They become your next of kin, there's all sorts of things that come into play. There are potential claims under the will. So it does have legal ramifications."