Former UK prime minister Boris Johnson will cut short his Australian book tour after cancelling a Melbourne event this week.

Johnson was due to speak at a dinner at the Sofitel hotel in Melbourne on Saturday to promote his political memoir, Unleashed. The event was to follow another show in Sydney, which will go ahead on Friday.

Australian publicist Max Markson, who has been promoting the tour, confirmed the Melbourne cancellation to Guardian Australia.

“Due to unforeseen circumstances, Mr Johnson has to travel back to the UK a day earlier than planned, therefore regrettably, the Melbourne event has had to be cancelled,” he said in a statement.

“We wish to apologise for any inconvenience caused, and wish to articulate that all Melbourne tickets are transferable to Sydney, or fully refundable.”

Asked if demand for ticket sales was behind the reason for the cancellation of the Melbourne event, Markson said “no”.

In a social media video message to promote the event last month, Johnson said he was “hugely excited” to be travelling to Australia.

The event page for Johnson’s Sydney event, to be held at Doltone House, said guests will be joined by the former British prime minister for a “long lunch”.

“Hear directly from Boris Johnson as he talks about all the big decisions during his time as Leader – the challenges he faced from Covid-19; riots; crime; the London Olympics – and much, much more,” the event page said.

“There will also be an interactive Q&A, giving you the chance to ask your big questions, and gain further insight into his experiences and perspectives.”

The cheapest tickets for the events were priced at $295 each with a meal, or $99 without one.

Johnson’s book, Unleashed, released in October, chronicles his time in politics, including his role in Brexit.

Prior to becoming prime minister, Johnson was mayor of London from 2008 to 2016 and foreign secretary from 2016 to 2018 under Theresa May’s Conservative government. He became prime minister in 2019.

He announced his resignation as prime minister in 2022, after pressure from within the Conservative party and the departure of several ministers.

Johnson resigned from parliament last year after an investigation into the UK’s Partygate scandal found he deliberately misled the parliament.

Johnson rejected the findings, arguing the parties were aligned with public health rules at the time. He labelled the investigation a “witch-hunt.”