Updated 5.10pm: Labour's continued capital gains tax missteps provide more ammunition for the prime minister.

David Cunliffe's backtracked on comments yesterday, that after a parent's death, their children would have one month to sell off the family home, before the tax kicks in.

But he's unable to say what the actual grace period would be, saying that'll be up to an expert panel.

John Key is painting Labour as heartless, and has dubbed the policy a 'death tax.'

"So you've just lost your parent or parents, and Labour is saying your number one priority should be going off to your accountant. I would have thought it would have been dealing with the emotional stress and memories."

Labour's David Parker has claimed John Key's aggression prompted David Cunliffe's hesitation in the Press leaders debate.

David Cunliffe avoided answering the question until after the debate when he could check his facts.

His deputy David Parker says it was the right thing to do.

"In fairness to David, he thought Key had it wrong but Key was being so aggressive that he thought he'd better check before he put Key down on the issue. DC didn't do anything wrong there."

Key hypes tax plan

John Key’s dismissing talk of double standards, as he continues to hype National’s tax cut plan while attacking Labour for failing to disclose its full capital gains tax to the public.

Mr Key says he’ll announce more of National’s policy on Monday, but in the meantime, he’s demanding David Cunliffe come clean over how the family home would be subject to Labour’s tax.

John Key says the parties are in totally different situations here.

He says Labour's had its policy for nearly four years, and Mr Cunliffe was its architect, so voters shouldn't have to wait until after the election to find out how it works.