Mayor Boris Johnson will tell the Home Affairs Select Committee later how public confidence in policing can be restored.
It comes after revelations that undercover police officers sought to smear the family of Stephen Lawrence.
Met Police Commissioner Sir Bernard Hogan-Howe will also be appearing.
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Rebecca Casserly was on her way to buy a coffee in north London when her phone was suddenly snatch from her hand by a man riding a bike.
Lee Curley took more than 120 pictures and videos of his attacks on the girl, said to be under the age of 13.
Council workers uncovered the AK-74 concealed in the undergrowth.