Superintendent Barry Taylor, national manager of operations, said after the time off in lieu buy-back, the squad had underspent for the year.
"Police is constantly prioritising its resources according to operational requirements and the difference has been met from within existing operating budgets without impacting on other services," Mr Taylor said.
Police Minister Anne Tolley said police were responsible to her for living within their total allocated budget and they were doing that.
"The DPS perform an important function in protecting dignitaries, and the Police Commissioner is responsible for its operational management. I trust police to deploy DPS officers as they see fit, and politicians cannot and should not interfere in any of these decisions."
After previous budget blowouts, Opposition parties accused the Prime Minister of being partly responsible for the increased spending because of what they claimed was an overuse of security details, even within Parliament.
Labour police spokeswoman Jacinda Ardern told the Herald Mr Key's use of the DPS was unprecedented. "Even from what we have observed within Parliament, there seems to be an increase in staff."
Ms Ardern said former prime ministers did not rely on so much security and it was up to Mr Key to justify it.
"We're sort of working in the dark because we don't really know what sort of threats or reasons there could be [for the increase]."
A spokeswoman for Mr Key said he had nothing to do with the decisions police made on security.
"The Prime Minister considers his protection staff to be extremely hard-working professionals," the spokeswoman said.
DPS officers are based in Auckland and Wellington and provide VIP protection for the Prime Minister, Governor-General, guests of the Government and embassies and consulates.