Boris Johnson had been due to address Tory MPs and party members during a Northern Research Group event in Doncaster, South Yorkshire, on Friday.
But in the afternoon, he tweeted a picture of himself with Ukrainian President Volodymyr Zelensky in the war-torn nation’s capital – his second visit since Russia began its invasion in February.
His last-minute cancellation at the Tory conference comes after the Conservative candidate for the Wakefield by-election compared trust in the party amid the resignation of disgraced former MP for the constituency, Imran Ahmad Khan, to faith in GPs despite the crimes of mass murderer Harold Shipman.
Mr Khan resigned after being found guilty of groping a teenage boy, and Nadeem Ahmed will be running to replace him in the West Yorkshire seat in less than a week.
Mr Johnson’s trip to Ukraine was kept a closely guarded secret, with Conservative MP Jake Berry telling reporters at 1pm he did not know why the PM was not there but that the reason would be clarified “in the next hour”.
When asked why Mr Johnson had pulled out, Mr Berry, who represents Rossendale and Darwen, said: “I don’t know.
“When you have the Prime Minister of your country who is going to come and attend your conference, which is brilliant, and he’s a huge supporter and has been in touch to wish us all the best, occasionally things happen, which I understand will come out in the next hour about why he’s had to cancel the whole of his tour to the North of England today.
“It is an unfortunate thing but at the end of the day, he’s Prime Minister of our country and things come up.”
Responding to reports that some Tory MPs reacted with fury to Mr Johnson’s absence and accused him of failing a test of outreach to his colleagues, chief secretary to the Treasury Simon Clarke tweeted: “He is literally leading high level talks with the President of Ukraine, a nation still fighting for survival in large part thanks to the leadership @BorisJohnson has shown.
“I think people seriously need to check their priorities”.
Earlier, Labour’s shadow health secretary Wes Streeting tweeted: “Absent leadership pretty much sums up this Government’s approach to the country’s problems”.
Communities Secretary Michael Gove appeared at the conference via video link in Mr Johnson’s place.
Downing Street had declined to discuss the Prime Minister’s whereabouts on Friday or over the weekend before releasing details of his Kyiv visit just before 4pm.
Mr Berry previously described the conference as “a fantastic chance to discuss ideas that will help us Level Up the North” and give members “the opportunity to shape our policy asks from Government”.
Earlier on Friday, business minister Paul Scully distanced himself from Wakefield candidate Mr Ahmed’s Harold Shipman comment, telling LBC: “It’s not a comparison I would have made.”