Recent troubles within the Act Party have once again raised questions over their reliance on Rodney Hide's Epsom electorate.
Their concerns are likely to be heightened after Prime Minister John Key confirmed National would stand a candidate there.
Act's five MPs are in Parliament only because Mr Hide holds the seat. The party won only 3.65% of the vote in 2008 -- short of the 5% threshold otherwise needed to win seats.
Mr Hide won the Epsom seat with 21,102 votes in 2008.
His nearest competitor was former National minister Richard Worth with 8220 votes.
Dr Worth, in Parliament as a list MP, resigned in June last year under a cloud after Prime Minister John Key said he had lost confidence in him.
Until today National had not confirmed whether it would stand a candidate in the electorate.
Mr Key said it would, although he did not speculate on who it would be.
"National will put up a candidate for the Epsom seat, just as we did in the 2008 election.
"There's a long way to go until the next election and we'll be going through the candidate selection process in due course," he told media.
Mr Hide said neither his seat nor Act's position in Parliament could be taken for granted.
"That's why we work so hard to do the good job that we do."
He said the National Party had made it clear to him that it would be standing a candidate in Epsom.
"It's not for the Act Party, or the National Party, or the Green Party or the Labour Party to say who should be the MP for Epsom, it's Actually up to the people of Epsom. That's why I have to work so hard."