When Prime Minister Jacinda Ardern meets her embattled British counterpart Theresa May tonight (NZT) she will be hoping the latter will not be too distracted by the Brexit turmoil in her own country to discuss trade.

Ardern, who is in the UK for a brief visit before heading to the World Economic Forum in Davos, Switzerland, has put trade at the top of her agenda, saying free-trade agreements with both Britain and the European Union are priorities.

May is in the midst of the fallout from her defeat in the House of Commons last week over her plan to leave the EU and following her meeting with Ardern at 10 Downing St, May is expected to go back to Parliament to tell MPs how she plans to proceed.

Ardern will be seeking a reassurance from May that New Zealand will be no worse off, including in trade, following Britain's departure from the European Union.

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"My visit to the UK is an opportunity to underline New Zealand's position as a natural and long-standing partner for the country as it redefines its global role post-Brexit," Ardern said in a statement last week.

While May will hear Ardern's reminder that New Zealand is high on the list of countries Britain wants to negotiate free trade agreements with, it likely won't be high on her list of short-term priorities.

Before Britain is in any position to negotiate free trade agreements, the House of Commons must first agree on a way forward or face a so-called "hard Brexit" on March 29 – that is leaving the European Union with no plan.

Options include a new referendum, May softening her "red lines", the key issues she has opposed in negotiations, or possibly seeking an extension to the exit date.

While May has dropped out of attending the World Economic Forum (WEF) this year to deal with the Brexit issue, Ardern will be there, along with Finance Minister Grant Robertson.

Following a morning of talks on the sidelines with other world leaders to push New Zealand's trade agenda, Ardern will meet naturalist and broadcaster Sir David Attenborough on Tuesday afternoon (early Wednesday NZT).

The pair will then be part of a panel discussion chaired by former US vice-president Al Gore.

The discussion, which is being livestreamed on the WEF website, will focus on how leaders can take action to safeguard the planet in the face of climate change, pollution and habitat loss.

Ardern will end her first day in Davos attending the chairman's dinner at the Morosani Schweizerhof hotel as a guest of the WEF's founders Klaus and Hilde Schwab.

Ardern is at Davos for two days before heading to Brussels for meetings with European Council and Commission leaders.