An appeal to the Privy Council by convicted murderer Mark Lundy is to begin on Monday.
Lundy was given permission earlier this year to have the case heard in the London court.
Thirteen years ago Lundy's wife, Christine, 38, and daughter, Amber, 7, were bludgeoned to death in their Palmerston North home.
Lundy was arrested six months later and in 2002 jailed for 17 years after being found guilty of double murder.
An appeal against his conviction in 2002 was rejected by the Court of Appeal, which extended his sentence to 20 years.
The Privy Council hearing has been set down for three days.