British Prime Minister Boris Johnson has lost his game of Brexit "chicken" with U.K. opposition parties and the European Union, according to Niall Ferguson, a senior fellow at the Hoover Institution at Stanford University.
His comments come at a time of heightened political uncertainty in the U.K., with the new prime minister under immense pressure to deliver Brexit with 55 days to go before the country is scheduled to leave the European Union.
When asked whether Boris Johnson and Dominic Cummings, the adviser behind the prime minister's high-stakes Brexit strategy, had overplayed their hand, Ferguson replied: "I think that they played a game of 'chicken,' not only with the Europeans but with their opponents in parliament and they lost."
"It is as simple as that."
Speaking to CNBC's Steve Sedgwick at the Ambrosetti Forum in Italy on Friday, Ferguson said of Johnson: "I don't think that there is any way out for him that I can see other than to resign because currently he is a hostage."
"He is under house arrest in number 10 Downing Street with power having entirely shifted to the House of Commons."
An alliance of opposition parties and rebel lawmakers from the ruling Conservative party wrested control of the lower house of parliament on Wednesday. The move could force Johnson to seek a three-month delay to Brexit.
Johnson has repeatedly insisted he would not seek to further delay Britain's exit from the EU, saying on Thursday that he would rather be "dead in a ditch" than ask for another deadline extension.
Brexit remains a deeply divisive issue in the U.K., more than three years after the world's fifth-largest economy voted to leave the bloc. And, as the country appears poised for a snap election, options range from a so-called "no-deal" Brexit scenario to abandoning the whole process altogether.
Johnson was dealt another blow on Thursday, when his brother Jo Johnson announced he was quitting the cabinet, citing "unresolvable tension" between his family loyalty and the national interest.
When asked by reporters whether he would resign too, the prime minister said he was focused on getting the country ready to leave the EU on October 31.
Sterling hovered close to a six-week peak of $1.2353 Friday morning, amid hopes Britain could avoid departing the EU without a deal.
The U.K. currency had fallen to a near three-year low earlier in the week, after the new prime minister stoked fears of a so-called "no-deal" Brexit.
"As long as the opposition parties can maintain unity and coordinate with his opponents within the Tory party, I don't think he has any alternative but to resign," Ferguson said.