National MP Chris Bishop is preparing to speak as sources tell the Herald conversations are occurring about a change in party leadership.

Bishop, who has been speculated as a potential contender though has denied such ambitions, is at the opening of Te Mahia Station level crossing in Auckland.

He’s expected to speak to media afterwards.

It follows revelations from the Herald last night that discontented National MPs were hitting the phones on Monday about a potential leadership change.

One MP said, “there’s going to be change” in the top job, but it was a “question of who is going to be it”. They cited senior National MPs Chris Bishop and Erica Stanford as potential front-runners.

Both Bishop and Stanford have previously denied ambitions for the leadership, though caucus sources have said they believe both MPs are contenders despite their public statements.

Other National MPs spoken to expressed openness to change, but did not say they were definitively in either camp, while an MP in Luxon’s camp disagreed with change.

Concern over Luxon’s leadership has been rumbling away all year, with the leader forcing a confidence vote on himself in April, which he survived.

The Herald has been told by MPs that they believe the margin of that vote was 27 to 22 in favour of Luxon; however, the figure is kept confidential to the party whips.

When the Herald put that vote margin to Luxon on Saturday, he responded: “All I know is I have the support of my caucus ... I just say to you I have the support of my caucus.”

The latest round of speculation appears to have been triggered by the leader’s out-of-the-blue announcement last week that he wanted a referendum on the country’s electoral system if re-elected.

That came as a surprise to his own MPs, who gave differing answers afterwards as to whether it was party policy.

It also followed Luxon belittling the concerns of business at a Rotorua event – for which he later apologised – and a story from the Herald revealing he’d used a Defence Force plane to get home from a National Party fundraiser.

On Sunday, Luxon and his finance spokeswoman Nicola Willis fronted a press conference to talk about the party’s fiscal rules, which included keeping taxes low, but couldn’t rule out increasing taxes.

Luxon less than 24 hours later clarified potential tax increases were limited to fuel excise, an accommodation levy, and a tax on banks.