Taxpayers forked out close to $12,000 for an event celebrating former Foreign Affairs Minister Winston Peters' tenure in the job.

It's an event that, according to Foreign Affairs Minister Nanaia Mahuta, Peters did not even want.

But it went ahead nonetheless, with a group of roughly 100 MPs, diplomats, their spouses and senior members of the public service in attendance.

Prime Minister Jacinda Ardern was also there, and paid tribute to Peters, her Deputy Prime Minister between 2017 and 2020.

Peters and his New Zealand First Party didn't get enough votes to return to Parliament at last year's election.

The $12,000 bill for the event has attracted the attention of the Taxpayers' Union, which has called on Mahuta to explain the sum.

"Many taxpayers could think of far better uses of $11,733 than a party thrown for a politician, by politicians," said Taxpayers' Union executive director Jordan Williams.

But Mahuta won't comment. Instead, her spokesman directed all questions to the Ministry of Foreign Affairs (Mfat), which said the event was aimed at communicating New Zealand's "approach to international affairs" to diplomats, which was customary around the world.

This is despite describing the December 1 event as a "celebration of Rt Hon Winston Peters' tenure as Foreign Minister", on Mfat's website.

And the majority of Mahuta's speech was about Peters and his "legacy" as a minister.

• Winston Peters misty-eyed as PM pays tribute at Parliament farewell

"Tonight is about saying thank you to the Right Honourable Peters and his team."

The event was invitation-only and closed to most media.

But it's where Peters made his so-far only public comments about leaving Parliament.

"It's been a privilege to be Foreign Minister, it has also been fun," he said in his speech, now up on Mfat's website.

According to an Official Information Request (OIA) for the Taxpayers' Union, the bill covered the cost of catering, technical/AV and furniture hire.

The document also shows the ministry covered half of the event's cost – some $5866.

The other half was paid for by the office of the Minister of Foreign Affairs.

The Herald asked Mfat if the $12,000 cost was reasonable to farewell a politician but it did not respond.

The Mfat spokesperson said the event was also to host New Zealand's diplomatic corps and such events are "customary all around the world".

The event, the spokesperson said, was a way for Mahuta to "directly and clearly" communicate New Zealand's approach to international affairs with the diplomatic corps.

But in her speech – which is also up on Mfat's website – Mahuta said: "Tonight is a rare opportunity that we get to stop, pause and say thank you for the significance of the contribution of the Right Honourable Winston Peters."

She even told those in attendance that Peters' "did not want the night to happen" and she had to "plead with him ... to host him and say thank you".

"Yes, in his role in foreign affairs but also as a parliamentarian for New Zealand."

Although he did use it as an opportunity to thank Ardern and reflect on the past three years, Peters' speech mainly focused on foreign affairs issues.

"Our diplomats are more vital than ever as our post-Covid world accentuates regional and global challenges."

He also used the occasion to wish Mahuta the best for her tenure as Minister of Foreign Affairs.

Peters did not respond to requests for comment on this story.