Foreign Affairs Minister Winston Peters is sticking to his desire for a free trade deal with Russia at some point in the future, saying even North Korea could be one day be an option.

Photo: RNZ / Craig McCulloch

Mr Peters made the comments in London at the end of the Commonwealth Heads of Government meeting.

Mr Peters has also been in Brussels this week and insists the Europeans he's met have no concerns about his views.

A Russian trade deal was not on the government's agenda, but could be one day if Russia came to its senses, Mr Peters said.

Even North Korea could be an option, he said.

"EU first and other countries, but we hope in the long-term, we've got a free trade deal with North Korea - but not at the moment."

There would be no progress towards a deal any time soon given the suspected nerve agent attack in Syria and its ally Russia blocking a bid for an independent investigation, Mr Peters said.

"It's rather axiomatic - if you're engaged or assisting a party ... involved in a chemical weapon attack, then all such progress must stop right there."

Prime Minister Jacinda Ardern said none of the world leaders she'd met during her week-long tour of Europe had raised the matter of a Russian trade agreement.

"Obviously the outcome of each of those [meetings] has been they are supportive of New Zealand's endeavour to have a mandate [for an EU trade deal] on the 22nd of May," she said.

Mr Peters said the leaders had also discussed the prospect of putting together the bones of a Commonwealth free trade agreement, before the United Kingdom left the European Union.

The deal could be modelled on the new Trans Pacific Partnership, said Mr Peters.

"Well there's a whole lot of excitement about that and how we might begin to put some flesh to an idea, which was levelled two years ago, but since 23 June 2016 it's become real and so that was very exciting."

International Business Forum executive director Stephen Jacobi said a deal between Commonwealth nations could help New Zealand forge business ties with countries it had been unable to previously.

A Commonwealth deal would link New Zealand to India - which has resisted efforts to enter into a trade deal between the two countries, he said. New Zealand would also gain access to many African nations.

But Mr Jacobi warns any deal would take a long time to negotiate and finalise.

Meanwhile, Ms Ardern said she was sure the Prince of Wales would serve the Commonwealth well when he takes over as its head.

Commonwealth leaders - including Ms Ardern - have confirmed that Prince Charles will one day take over that position from the Queen after a full-day private retreat at Windsor Castle.

Leaders had talked about the environment - including the health of oceans - at their meeting, as well as agreeing to condemn the use of chemical weapons, Ms Ardern said.

"I made particular comment around the need for practical outcomes with a focus on things like the environment and climate change.

"I also talked about the future ambitions of the Commonwealth and the need for us to do further work on issues of inclusion, particularly for LGBTIQ communities."

The majority of the Commonwealth countries still criminalise sexual acts between consenting adults of the same sex.