Labour's Diane Abbott pulled out of a live radio election debate against Home Secretary Amber Rudd on Tuesday following another bungled interview.
Ms Abbott was set to go head-to-head with the Conservative and other rivals on BBC Radio 4's Woman's Hour programme but pulled out due to illness.
It cme after another difficult interview in which she struggled to answer questions about her own home affairs brief, with her leader Jeremy Corbyn facing questions over whether she would be up to a job in government.
The BBC announced this morning that shadow Foreign Secretary Emily Thornberry would stand in for Ms Abbott with minutes to go before the programme was broadcast.
In an interview with Sky News on Monday night, Ms Abbott said it was time to "revisit" the advice in a report into London security by the former Metropolitan Police Authority chairman Lord Harris, but was then unable to give any of the specific details of it.
Asked which part she was endorsing in the uncomfortable interview, she simply replied: "I just think it's about preparedness and resilience."
Ms Abbott denied reports that the Labour leader and shadow chancellor John McDonnell were taking steps to keep her off air for the remainder of the election campaign.
"I am here. I have just come from doing another media interview. I'm going on to do another media interview. There is no truth in the idea I'm not in the media," she told Sky.
In a previous excruciating interview Ms Abbott struggled with figures around Labour's policy of introducing 10,000 new police officers, and later appeared ill-briefed over the losses the party suffered in local elections.
Ms Abbott was set to appear in the London Evening Standard's election hustings on Tuesday evening, though it remained unclear if she would recover in time.
