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
The Metropolitan Police said the building material was found in the force's former training facilities.
The toddler was seriously injured when one of the cars rolled and trapped him between the vehicles in a private car park
The millionaire winner is one of 10 lucky players from the EuroMillions Mega Friday draw on 28 November.