Leaders' showdown: Will the third debate be the decider?

Labour leader David Cunliffe will be looking to turn the tables on National's John Key at the third head-to-head debate - with the battleground likely to be tax again.

Mr Cunliffe was caught out on capital gains tax at last week's debate, and has been in lockdown for almost two full days to prepare for tonight's showdown on TV3 at 8.40pm.

He desperately needs a circuit breaker to shore up Labour's vote, which has continued to slip through the campaign. He indicated he would try to get that by tackling National's tax policy.

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"I've certainly got more policies to prep up on than he has," he said.

"There are only 30 pages of policy on National's website, close to 200 on ours and all he's got is a $5 tax cut maybe in three years' time. A bottle of milk if you're lucky, half a block of cheese and that's if it's not used to pay off debt."

Join Claire Trevett at 8.40pm for live coverage of the debate

Mr Key spent the morning campaigning and announced National's corrections policy at Wiri Prison before disappearing to prep himself.

He said on TV3 this morning that he expected the two will "be butting heads on all the main issues".

"He'll want to talk about tax and so will I - he wants to add five new taxes and we want to cut taxes. So there's a nice contrast there."

He defended the lack of detail in the tax policy saying he expected headroom for about $1 billion of tax cuts and as wages increased, the tax brackets had to be looked at. He said despite the amount, "it matters that we are trying to cut taxes at a time Labour is looking to increase them."

Mr Key had a similar timetable before the One News debate - the first time the two had gone up against each other. Mr Cunliffe had held his own on that occasion while many observed Mr Key appeared flat. It was in the midst of the fallout from Dirty Politics - and the day after Judith Collins had resigned as a minister.

Mr Cunliffe also repeated his underdog claim of the first debate, saying he was new to the leaders' debates while Key was experienced "so I'm just being realistic about the fact it's an important debate".

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