Diane James has quit as leader of Ukip after just 18 days in charge.
The 56-year-old said it had become clear in discussions with party officials that she did not have "sufficient authority" to push through changes which she had planned.
Scottish Conservatives leader Ruth Davidson said that the resignation of Ukip leader Diane James shows the party is a "shambles".
She told ITV's Good Morning Britain: "I have to say I was surprised when I heard the news last night. I thought Sam Allardyce was holding the record this week for resignations but it turns out that Diane James has taken his crown."
Referring to the leadership contest in the summer, which saw favourite Steven Woolfe expelled from the race, Davidson added: "You see Ukip as a shambles over the summer, a shambles now with their leader not even lasting three weeks."
Diane James has quit as Ukip leader before most people knew who she was. What happened?
Bill Etheridge, who stood against Diane James for leadership, said he was disappointed at her resignation adding she was supported by MEPs.
She has been in the role less than three weeks.