Winston Peters tips leadership challenge for British PM Theresa May

Acting Prime Minister Winston Peters is tipping a challenge to British Prime Minister Theresa May's leadership after the resignation overnight of her foreign secretary Boris Johnson.

Peters, who is also the Foreign Minister, told Newstalk ZB's Larry Williams this morning that would not comment on whether he thought Johnson would make a good prime minister in the future.

"I can't answer that question but I can tell you there's every likelihood that there's a spill on, as the Aussies say in UK politics and it's been coming for a while."

A leadership spill in Australian politics is a declaration that the leadership of a parliamentary party is vacant.

Johnson resigned from his position as British foreign secretary in a fresh blow for May's government.

Johnson followed Brexit minister David Davis in resigning over May's master plan for Britain's future outside the European Union.

Davis and his deputy quit just two days after May announced she had finally united her government behind a plan for a divorce deal with the EU.

Johnson gave a scathing verdict on May's Brexit plans in his resignation letter which said the "Brexit dream is dying, suffocated by needless self-doubt".

Peters, who met Johnson in April for talks, said he was saddened by his resignation.

"It's very sad on a personal basis because I think he's something that's lacking in worldwide politics, a man of true character, fascinating, bright, intelligent, and we had a good relationship."

Peters said British politics had not seen the end of Johnson yet.

"I kind of think there's more to come from Boris in the future and this is just the beginning of what is quite a momentous time in British politics."

- With agencies