United Future leader Peter Dunne says he is probably the most lobbied MP in Parliament, as his party has held the balance of power for more than 10 pieces of legislation this parliamentary term.
Mr Dunne's crucial vote has sealed major law changes including the Government's flagship asset sales legislation. On the other hand, the minister will oppose Government law changes such as the introduction of charter schools, and has helped private member's bills from the other side of the House to get over the line.
With Act usually voting along the same lines as National, the ruling party relied on United Future's vote for a majority in the House.
Mr Dunne admitted that he wielded power that was disproportionate to his party's one-seat representation in Parliament.
"I'm quite conscious of ... not trying to overplay the hand. On the other hand, you don't want to be silent either.
"I'm one out of 121 and I've got to have a rational basis on which to make these decisions. The way in which I approach this these things is not capricious."
The minister said he applied three criteria to each piece of legislation. He considered whether it was part of his party's confidence-and-supply agreement with National, or whether it fitted with United Future policy. If it did not fit either of these categories, he decided whether it was a "common sense" law change.
Mr Dunne said that two Labour bills - extending paid parental leave and "Mondayising" public holidays - both fitted with United Future policy.
His vote helped the holidays bill into law by a single vote.
It would also help the paid parental leave bill get a majority, though the National-led Government has said it would veto a law change. Mr Dunne was likely to hold the key vote if the Government struck a deal with SkyCity for the construction of a convention centre, which was expected to require a law change.
He said he was keen for Auckland to have a world-class convention centre, but he has also opposed an increase in the total number of pokie machine licences.
"The test will be the extent to which those two positions can be reconciled in the legislation that emerges."
Mr Dunne's special position meant he could have significant influence on contentious legislation.
He initially planned to oppose a bill which aimed to deter people-smuggling.
The National-led Government had a majority on the Immigration Amendment Bill with the support of Act and the Maori Party, but wanted all of its coalition partners onside.
Mr Dunne forced National to change the definition of a mass arrival of refugees from 10 people to 30 people, and also to make changes which made the bill less punitive.
His key vote has also made him a lightning rod for criticism, in particular on the partial asset sales legislation.
Mr Dunne said he sometimes tired of being singled out for his voting pattern.
He suspected he was lobbied much harder than other MPs.
"It's not a position I sought. It was the way the numbers fell at election time. But what's important is to have a process."
Dunne's deciding votes
• Mixed Ownership Model Bill (passed 61 votes to 60)
• Climate Change Response (Emissions Trading and Other Matters) Amendment Bill (61-60)
• Minimum Wage (Starting-out Wage) Amendment Bill (61-60)
• Holidays (Full Recognition of Waitangi Day and Anzac Day) Amendment Bill (61-60)
• Social Security (Benefit Categories and Work Focus) Amendment Bill (61-59)
• Minimum Wage Amendment Bill (failed 59 votes to 61)
• Immigration Amendment Bill (supports, with amendments)
• Parental Leave and Employment Protection (Six Months' Paid Leave) Amendment Bill (supports)
• Legal Assistance (Sustainability) Amendment Bill (supports, passed 2nd reading 61-60)
• Plumbers, Gasfitters and Drainlayers Amendment Bill (supports, passed 2nd reading 61-60)
• Convention Centre legislation (supports in principle)