The Government has shifted the goalposts in its promise to deliver more frontline police after what seems like a slip of the tongue by Prime Minister Jacinda Ardern.

It promised to "strive towards adding 1800 new police" over three years but in a game of semantics, it is now saying it will deliver 1800 new trained recruits by next month.

The move has drawn the ire of the Police Association who say it is not good enough and that the Government has broken its promise to police.

Police Association President Chris Cahill said it came as a big surprise to members and made no sense. His union is angry because the 1800 was supposed to be on top of current numbers: a net increase in police numbers.

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"We were always very clear, it had to be on top … this is what police understood. We will hold the Government to account to keep its promise."

The Government has insisted that 1800 extra new officers was never a target, but an aspiration.

Police Minister Stuart Nash told Stuff last week numbers had increased by 893 officers - about 10 per cent since the start of the 2017-18 financial year. Full time constabulary staff currently sits at 9,732 officers.

He has repeatedly said the 1800 figure would take attrition into account and argued this on many occasions - as recently as Tuesday, during a Police Association conference:

"So far we have graduated around 1685 since becoming government, which equates to around 892 more staff over and above attrition. We said we would strive for 1800 and it is aspirational.

"We will deliver 1800 and even if it takes a bit longer, I give you an assurance that the money is there."

"My promise to you is that if we don't reach our numbers in three years, we will keep training new officers until we do reach this target – and then we will maintain this ratio."

So it came as a surprise to many when Ardern quickly responded "yes" after Opposition Leader Simon Bridges asked in the House on Tuesday, if the Government would reach its 1800 new police officers target this term.

The Government seemed to regroup for Question Time on Wednesday, forcing Nash to agree that the government would reach its aspirational 1800 target, not the about 900 he had talked about last week.

National's police spokesman Brett Hudson asked Nash if Ardern was correct. The minister replied that she was correct and the target would be met next month.

"I will also confirm that we've done it in under three years – in fact, just over two years."

Hudson asked Nash if he stood by his response to a written question, which confirmed that the measurement of the 1800 new police included attrition, and was currently running at well under 900.

But Nash only replied to say police attrition was about 3.8 per cent.

Deputy Prime Minister Winston Peters then piped up to say the coalition agreement promise was to only to add 1800 trained recruits, not extra police on the beat.

After Question Time, Nash said the prime minister and the deputy prime minister were the designated spokespeople for the Coalition Agreement.

"I have also been very clear that I want police to achieve real growth in the number of frontline officers to take account of attrition and turnover. Police are currently funded to address attrition. I expect them to achieve real growth of 1800 frontline officers."

Hudson said Nash had confirmed in writing to National that additional recruitment accounted for police officers who leave each year.

"The Prime Minister doubled down on this yesterday, promising there would be 1800 additional police on the force by next year."

He said it was an admission of defeat from the Government and a broken promise.