OPINION: The National Party is deliberately spreading misinformation that Labour is raising income tax - when it's not.

Bill English is sticking by the claim, when asked on Wednesday if he could say hand on heart that Labour will raise income taxes he replied: "From 1 April next year."

But a fact check shows this is not true. If National wins, tax are cuts planned for April 1 next year. If Labour wins, it will cancel the tax cuts - but it will not raise taxes.

Asked whether he was just making stuff up to hurt Labour Mr English said: "No, not at all, this is the law of the land."

Jacinda Ardern is calling it out.

"People want to hear a debate on the issues and that means the issues as they stand, not fake news," she said.

Bill English's explanation goes like this: because National has passed a law to bring tax cuts in, if Labour stops them before they start, that means they are raising taxes.

"It's really clear cut it's really clear cut someone on the average wage will pay $1000 more tax under Labour than they will under National," he said.

Jacinda Ardern says it's wrong. "National have claimed we are increasing income tax. We are not. We never have. We never did. For them to have campaigned on that to try and confuse voters was wrong."

The problem for Bill English is the Oxford Dictionary defines 'raise' as to "lift or move to a higher position or level."

This is what's called 'post truth politics', where deliberate lies and falsehoods reign supreme.

In the UK, there were lies about the cost of the European Union during the Brexit referendum. In Australia there were lies about health provider Medicare being privatised, and in America - all sorts of lies.

"It has been certainly been extraordinarily frustrating to see National run politics as usual, saying things that simply aren't true," Ms Ardern says.

And now, with Steven Joyce's false claim of a $11.7 billion hole, and false claims about income tax rises - post-truth politics is here.

The truth is - for Bill English - the truth on tax doesn't matter anymore.

Patrick Gower is Newshub's political editor.