Diane James has stepped down as UKIP leader after 18 days in the role, citing "personal and professional reasons".
"It has become clear that I do not have sufficient authority, nor the full support of all my MEP colleagues and party officers to implement changes I believe necessary and upon which I based my campaign," Ms James said in a statement published on her Twitter account.
"For personal and professional reasons, therefore, I will not take the election process further," she added.
The MEP became the first woman to lead the Eurosceptic party when she won the contest to replace Nigel Farage on 16 September.
Ms James, the front-runner throughout the leadership campaign, was backed by supporters of Mr Farage and UKIP's millionaire funder Arron Banks.
During the contest she promised to have a "laser focus" on the Brexit negotiations, but refused to set out any policies, insisting she did not want to make "policy on the hoof".
Thank you to all @UKIP supporters who attended my #MeetDiane meetings across the country over the summer. pic.twitter.com/EQf9rUXgKA
— Diane James (@DianeJamesMEP) October 4, 2016
