Britain's financial services minister John Glen resigned on Wednesday in protest against Prime Minister Boris Johnson, just days before the government is due to unveil a draft law to "reset" a post-Brexit financial sector.
"I can no longer reconcile my commitment to the role and to the financial services sector with the complete lack of confidence in your continuing leadership of our country," Glen said in his letter to the prime minister.
His resignation came after finance minister Rishi Sunak and health secretary Sajid Javid both announced their departures abruptly late on Tuesday, leaving Johnson clinging to power on Wednesday as more ministers also resigned.
Britain's financial sector, one of its most important tax-raising industries, was largely cut off from the European Union after Brexit, with banks and insurers now piling pressure on the government to buttress the City of London's global competitiveness.
Glen, who often joked he was Britain's longest serving City minister, was first appointed in January 2018.
He has undertaken over 30 public consultations and reviews on post-Brexit financial reforms.
As the EU moves ahead of Britain in writing new rules for sectors like crypto, the financial industry has urged the government to speed up the pace of reform, whose timing has now been thrown into doubt by the political uncertainty.
Sunak had been due on July 19 in a first "State of the City" speech at London's Mansion House to set out a new financial services law to ease rules on insurers, capital markets and encourage more retail investing by exploiting Britain's post-Brexit "freedoms" to write its own regulations.
Glen said last week the planned bill would mark a new era for financial services in Britain, with reforms such as easing burdensome rules on insurers to invest in infrastructure.
Reforming financial services remains one of the big Brexit narratives and therefore will not go away, a senior British banker said.
"At worst I think that gets slowed down a bit," the banker said, speaking on condition of anonymity.
The finance ministry had no immediate comment on whether plans to set out a new financial services bill this month would still go ahead under Britain's new finance minister, Nadim Zahawi.