Shadow home secretary Diane Abbott has pulled out of a radio programme after an embarrassing interview on Sky News with Dermot Murnaghan.
Ms Abbott was unable to answer questions on recommendations made in a key counter-terrorism review in October about how best to prevent London from terror attack.
In a series of vague answers after long pauses, it became clear that Ms Abbott was unable to recall details of the review by Labour's Lord Harris.
Despite insisting she had read the review, commissioned by London Mayor Sadiq Khan, Ms Abbott faltered on questions about merging police forces and putting up security barriers.
Dermot Murnaghan: "What do you think about the amalgamation of various police forces in London?"
Diane Abbott: "You mean the idea that they should work more closely together?"
Dermot Murnaghan: "Well he suggested they should amalgamate…"
Diane Abbott: "Well I think that's an interesting idea but I think you would find resistance in some part of London to the amalgamation."
Dermot Murnaghan: "Have you actually read the report?"
Diane Abbott: "I have."
Dermot Murnaghan: "OK. What about the physical resilience?"
Diane Abbott: "Mmmmmmmmmm. Yes. I mean I think physical resilience. I think that…"
Dermot Murnaghan: "Yes but there was a specific aspect of physical resilience…"
Diane Abbott: "Well I think that physical resilience is important."
Dermot Murnaghan: "Yes, well but the specific aspect was he talked about putting up more barriers in light of the Nice attack…"
Diane Abbott: "Yes, we are now putting up barriers on, erm, bridges and you would think we might have done that before…"
Ms Abbott was booked to appear on Radio 4's Women's Hour this morning but pulled out at the last minute citing "ill health". Shadow foreign secretary Emily Thornberry appeared instead.
She was later scratched from an Evening Standard hustings. The newspaper's editor, former Chancellor George Osborne, tweeted: "It's not like someone who wants to be Home Sec has much to talk about these days."
A spokesperson for Ms Abbott said: "Ms Abbott will not be talking about her health at this time. There can be no more distractions from the real issues of this General Election.
"Ms Abbott will be joining Labour party colleagues to get the vote out on Thursday."
The shadow home secretary has suffered from a series of embarrassing interviews during the election campaign, in which she has struggled to answer questions on her brief.
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There have been suggestions that Jeremy Corbyn and John McDonnell's teams have attempted to keep her off the airwaves in recent days.
However, Ms Abbott, who had arranged the interview on Sky News herself, denied there were concerted attempts to stop her appearing, saying: "No, that's why I'm here this evening."
In February, Ms Abbott missed a politically awkward vote on triggering Article 50 because of a migraine.
Cabinet minister Priti Patel said: "Jeremy Corbyn wants to make Diane Abbott home secretary in just two days but is hiding her away from voters.
"The woman who would be in charge of our police and the intelligence services cannot even be trusted by Jeremy Corbyn and John McDonnell to go on the airwaves to explain their shocking record on national security."