Theresa May's premiership is hanging by a thread as a high-profile Cabinet minister quit and a growing revolt over Brexit looked set to force the British leader from power.

Andrea Leadsom resigned late on Wednesday, saying she no longer believed the government's approach will honor the result of the 2016 referendum. May said she was "sorry" Leadsom had quit, while rejecting her reasons for doing so. The premier's office said she would stay focused on delivering Brexit.

Leadsom and other ministers spent much of Wednesday in private talks plotting to kill May's last-gasp plan to use a possible second referendum to get her divorce agreement through Parliament. As the pro-Brexit faction within May's Cabinet discussed how to coordinate their revolt, the most senior rank-and-file members of her Conservative Party held a crisis meeting to weigh up whether to throw her out.