The most likely result of the counting of the special votes tomorrow will be for Labour and the Greens to gain at National's expense - a result that will not change the ability of either side to form a government with NZ First but will help strengthen Labour's arm.

Gaining a seat or two on the left will help Labour's ability to form a stable Government by giving it a more comfortable margin than one seat for a majority.

The left wing parties traditionally do better in the special votes than on election night and it would take only a small shift in the 384,000 special votes for the Greens and then Labour to gain and for National to drop.

Electoral law expert Graeme Edgeler said it was highly unlikely either Labour, the Greens or NZ First would drop a seat unless they did significantly worse in the special votes than on election night which would buck the trends of past elections.

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The Greens will pick one up if they get about seven per cent of the special votes compared to the six per cent they got on election night while Labour will pick up one if it can get about 40 per cent of the special votes - its election night result was 35.8 per cent.

The Greens and NZ First would have to be on about two percent and Labour below 34 per cent to drop a seat. There is a chance NZ First too could pick up a seat - but it would need to do slightly better than its election night result of 7.5 per cent and traditionally does not fare as well in the special votes.

For National to hold its 58 seats there is very little room for it to slip in the specials compared to its election night result of 46 per cent.

If National lost two seats it would mean a National - NZ First grouping would muster 65 seats between them to the 63 of a Labour-Green-NZ First grouping. That is a much smaller gap than the 67 - 61 difference delivered on election night.

Edgeler said constitutionally picking up a seat would make no difference in Labour's ability to form a government but it would in practical terms.

"With 61 seats if one person crosses the floor you can't pass the Budget. That's a lot different from needing two or three people to cross the floor to do that. So yes, having a buffer of more than one is probably important if you're relying on three parties."

NZ First leader Winston Peters has put serious talks with Labour and National on hold until those votes were counted, saying it could impact on the outcome. However, he would not expand on what that might mean in his thinking.

While Peters has said National does not have the moral authority to form a government just because it got the highest share of the vote, it is likely he is wary of the one-seat majority on the Labour side of the equation.

Labour leader Jacinda Ardern has also expressed concern saying it would be more of a comfort if they could stretch out to a two or three seat majority.

Green leader James Shaw said he was confident of getting another seat and candidate Golriz Ghahraman was already attending caucus meetings because of the likelihood. He believed it would help ensure a Labour-led government.

"My reading is that [Peters] has placed a great deal of stock in the specials and you have to ask why would he do that, given the most likely outcome of the specials would be to at least partially even up the gap between National and the Labour-Green bloc. So I think it gives him a level of comfort in a constitutional sense that he can back the Labour - Green bloc because they are more or less even to National."

The votes include overseas voters and people who voted outside their electorates but this time there are more than usual because for the first time people could enrol and vote at the same time in advance voting booths.

That group too will be included in the special votes - and while Labour and the Greens in particular encouraged young first time voters such as students to take up that opportunity it is unknown what other voters also used that opportunity.

Labour's General Secretary Andrew Kirton believed that would benefit Labour and the Greens. If Labour picked up a seat it will get Bay of Plenty candidate Angie Warren Clark into Parliament - taking its representation from the Bay of Plenty to three MPs from none.

Even after the special votes are in there is the chance a candidate or party will apply for a judicial recount in an electorate or in the party vote if there is only a small margin between candidates or gaining an extra seat. Those must be lodged by Wednesday October 11.

Shaw said the party had not considered whether it would look at a recount but it would be something it would have to consider if it came within a

The electorate with the smallest margin is Ohariu which Labour's Greg O'Connor won by 679 votes over National's Brett Hudson. National would likely only consider a recount there if that margin halved into the 300s or lower following the special votes and recount of the election night votes.

The Maori Party may also be hanging onto the slim hope that the margins in Te Tai Hauauru and Waiariki are smaller than the election night margins of more than 1100 votes - although that would be a big turn around. Party President Tukoroirangi Morgan has refused to comment on the Maori Party's results until after the specials are delivered.

The final vote count in the 2017 election is expected to be released at 2pm tomorrow.