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 defence secretary Emily Thornberry will be appearing instead.

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.