The Prime Minister says he wants investigations to "get the full truth out" about "horrific" allegations, that police tried to smear the family of Stephen Lawrence.
An undercover police officer claims he was ordered to find information to discredit the family, Duwayne Brooks and campaigners.
He said it happened in 1993, just months after Stephen was murdered at a bus-stop in Eltham in an unprovoked racist attack.
Both the Home Secretary Theresa May and Mayor Boris Johnson spoke about possible criminal prosecutions of Met officers, if the claims prove to be true.
We have this report from our Senior Correspondent Ronke Phillips.
More top news
Five-year-old Yusuf Abdismad died from meningitis in January after a mix-up between emergency operators, it has emerged.
A strike by members of four unions, RMT, Aslef, TSSA and Unite, is expected to bring the Underground to a standstill tomorrow evening.
Official readings are recorded three metres in the air but a study found levels of nitrogen dioxide (NO2) were higher at pushchair level.