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."