"On the one hand I'm very confident about our position, we've had assurances both from the EU and British officials that existing access to this market will be maintained," Mr Key said.
"But longer term there are some parts of the export access that we have that we're very much looking to maintain or grow, particularly around things like lamb meat."
The prime minister said the UK had been a friend of New Zealand at the EU table, among other things advocating for New Zealand's entry into an EU free trade agreement.
"Those days are really over, they're no longer going to have a seat at the table ... Britain is no longer a voice to advocate for us, we need to do that on our own and for ourselves."
Mr Key said New Zealand had recommended the UK stay in the EU but there was no point in lamenting the Brexit decision.
"It does mean we have to put a bit more effort into pushing our European credentials.
"The challenge will be the likes of French farmers who are cautious about New Zealand, a little bit with Irish farmers as well as very large producers."
Mr Key cautioned about expecting a more open-door policy from the UK for New Zealanders wanting to live and work in Britain given that a key driver of the Brexit vote was a desire to curb migration, and an incoming British prime minister would be alert to that.
"New Zealanders have always enjoyed the rights to come and work here for a couple of years and we will want to maintain that and potentially ultimately open up the opportunities for more over time."
Mr Key said to achieve that New Zealand needed to stress its historical and family ties with Britain as well as the valuable work skills New Zealanders took to the UK.
- AAP