British PM Theresa May's move to formally trigger the Brexit process starts the two-year countdown before free trade talks with countries such as New Zealand can begin.

May signed the Article 50 Brexit clause on Wednesday night - triggering the process for the UK to leave the EU after the shock referendum last year.

Although the United Kingdom's immediate priority will be negotiating the terms of the exit - and its future relationship with the EU, when Prime Minister Bill English was in Europe in January, May promised New Zealand will be one of the first countries to negotiate a free trade agreement with the UK.

In a video released today, British High Commissioner Jonathan Sinclair pointed to preliminary trade talks already under way between New Zealand and the United Kingdom, saying the United Kingdom would be "truly global" - a "best friend" to other European countries: "And a country that reaches beyond our shores to strengthen relationships with old friends and new allies alike."

Advertisement

Although formal negotiations can not begin until after Britain has left the EU, there have been initial soundings.

English welcomed May's promise, but also made it clear the larger EU trade agreement was a priority in the medium term.

New Zealand and Australia are both in line to be among the first Britain turns to, partly because of the relative ease with which deals could be done and the need for Britain to show it can thrive on its own.

Heath Baker, the head of trade policy for Australia's Export Council, has urged Australia to get a deal with the UK as soon as possible - including possibly going for the "quick wins" first before hammering out a more comprehensive agreement later.

However, he also said the UK would not be Australia's most important trade deal. Australia is also negotiating a trade deal with the EU and Baker said it was important to note the rest of the EU "dwarfs the UK as a trading partner for Australia".