Labour MPs regarded it as a bit of a relief as they believed Mr Dunne had dragged the party closer to the centre on some issues around tax and family support.
Mr Dunne has been the political survivor of MMP even before MMP.
He has served as revenue minister in both Labour and National-led administrations and has spent the past nine years as revenue minister in the Helen Clark-led administration.
He will have been reading the polls, and without the television debate worm to lift his party's support around the country, Mr Dunne needed something to give his campaign a boost.
On current polling, only Mr Dunne will return to Parliament as a United Future MP.
To have some influence and stop up-and-coming National MPs feeling resentful they are being held out of a cabinet post by a one-man party similar to Progressive Leader Jim Anderton for Labour, he needs more MPs.
Tying himself to National is a gamble Mr Dunne is obviously prepared to take as the gap closes between the centre-left bloc and the centre-right.
At Parliament, Mr Key has welcomed a pledge of post-election support from Mr Dunne.
"National does anticipate that it will need support from other parties to form the next government, and it would welcome United Future's support. We see United Future as a natural support party for National. In fact, it is a preferred cab off the rank.
"National and United Future share similar views in a number of important areas of policy. We have no doubt that a stable and forward-looking support or coalition agreement could be reached after the election."
Messrs Key and Dunne said they had talked previously about the kinds of areas they could work on together and they included infrastructure, health and law and order.
What they did not say is that Mr Dunne favours further cuts in tax rates, something Finance Minister Michael Cullen would have been reluctant to entertain.
But Mr Dunne will get nothing much if he does not have more MPs.
Mr Key has acknowledged something long-time National Party supporters hate to admit - that he will need other parties to form a government"Once the New Zealand public has cast their votes, we hope to be in a position to sit down with United Future, and perhaps other parties, for further discussions," he said.
After ruling out New Zealand First leader Winston Peters, Mr Key is left with the Maori Party and Act New Zealand.
The Maori Party seems split about which party it might support.
One co-leader (Tariana Turia) seemed to be moving close to National on Wednesday when a couple of hours later, the other co-leader (Pita Sharples) was preferring Labour.
Mr Key ruled out working with Mr Peters because of all the controversy surrounding donations made to the party, where the money went and how it was accounted for.
Mr Peters was dragged before the privileges committee for a wet-bus-ticket telling-off.
Now, his party has been cleared by the Electoral Commission.
In an ironic twist, the Electoral Commission has found New Zealand First's party secretary did not break the law over incorrect returns last year, but Act did.
Act had repeatedly attacked NZ First over its alleged failure to declare cash and donations, and its leader Rodney Hide laid a police complaint relating to the 2007 return.
The commission last night released its decision saying while New Zealand First did not declare donations in 2005, 2006 and 2007, it was not asking for a prosecution.
However, the commission did find that Act got free office space from Sir Robert Jones for years until 2005, at a value of approximately $20,000 per annum.
The commission found the office space was a party donation and was not included in Act New Zealand's annual returns of donations for the relevant years.
It said Act must file amended returns but there would be no prosecution because the period in which that could happen had expired.
Mr Peters had tabled in Parliament a letter from Sir Robert outlining the donation of office space, but it was generally ignored until Dunedin South MP David Benson-Pope wrote to the commission.
The decision was released to Mr Benson-Pope and then posted on the commission's website.
Earlier, the Serious Fraud Office cleared Mr Peters of fraud.
It found money was used for the purpose the donors - Sir Robert and the Vela family - intended.
Mr Peters is also under investigation by the police, following a complaint by Mr Hide, but with the commission not asking for a prosecution, it is difficult to believe the police will find a case to answer.
Mr Key has ruled out Mr Peters, who has been found not guilty by the commission.
But he has indicated he could work with Mr Hide, the leader of the party that broke the law over incorrect returns.
Given the closing of the polls, it is unlikely anyone will hear Mr Key ruling out working with Mr Hide or any MPs he takes with him to Parliament should he retain his Epsom electorate.
Strange how what goes round comes round in politics.
• Prime Minister Helen Clark spent the weekend reminding voters to support Labour if they wanted a Labour government and not to vote for parties they thought she would like in Parliament.
National Party leader John Key admits he might need help to form a government and almost gives voters clearance to vote for United Future. Miss Clark takes a point.
