UPDATE 8.05AM: The numbers are being done in the National Party with Bill English expected by some of his colleagues to call it quits.

Newstalk ZB's political editor Barry Soper said it's a question of when, and the numbers are now being done for those who want to succeed him.

"A push against Mr English is unlikely. It is expected he will be allowed to go gracefully and with dignity but those behind him are now lining up to replace him.

"His deputy, Paula Bennett, might see herself as his natural successor but her own future in her current role is by no means certain, with some in the party seeing her as his Achilles heel during the last election and are not discounting she could be replaced as soon as next week's caucus."

One source told Newstalk ZB that if a move was made against Bennett in next week's caucus, it would be supported. 

Soper said the party's MPs will meet behind closed doors in Simon Bridges' electorate of Tauranga next Thursday and Friday.

"There is a general acceptance that Bill English was robbed of the Prime Minister's job by Winston Peters but senior MPs are now jockeying for support from their colleagues to replace him." 

He told Mike Hosking that there are several people who will be keen for the top job.

"Simon Bridges [has] shown in the past he's ambitious for leadership. And there are others [like] Paula Bennett, she would see herself as a natural successor but I think that's a very remote possibility. Judith Collins, she's still back there somewhere."