David Cameron has said a public inquiry into the work of undercover policing will "make sure we get to the truth".
The inquiry was commissioned after a report into the police inquiry into the murder of Stephen Lawrence uncovered evidence of corruption.
The Prime Minister added: "It should have not taken this long and the Lawrence family have suffered far too much."
Several of today's papers lead with strong headlines after the report into the police inquiry into the murder of Stephen Lawrence uncovered evidence of corruption.
The public inquiry announced today will examine the Special Demonstration Squad, the Metropolitan Police's undercover unit.
It was set up in the 1960s to infiltrate protest groups. One former member has claimed he had been told to find information to smear the Lawrence family.
ITV News correspondent Paul Davies has been looking into the background of the secret squad:
Almost 21 years after Stephen Lawrence was stabbed to death, the Home Secretary has ordered a public inquiry into undercover policing .Read the full story ›
Lord Taylor of Holbeach was overcome with emotion when speaking to the House of Lords about the Stephen Lawrence report today.
"Stephen Lawrence was murdered more than 20 years ago and it's deplorable that his family have had to wait so many years for the truth to emerge," the Home Office minister said, speaking opposite Baroness Lawrence, Stephen's mother.
"The findings I have set out today," he continued, his voice cracking, "are profoundly disturbing.
"For the sake of Doreen Lawrence, Neville Lawrence and their family, and the British public, we must act now to address these wrongs."
Our Senior Correspondent Ronke Phillips was with Neville Lawrence as he watched the Home Secretary deliver the report. He spoke about the fight for justice, and how it was far from over.
Stephen Lawrence's mother Baroness Lawrence fought back tears in the House of Lords as she said she and her family had endured "21 years of struggle" and there was "still more to come" following a review into the original investigation into her son's murder.
Scotland Yard deputy commissioner Craig Mackey said police would be "saddened" and "shocked" by the findings of the Ellison report:
There can be no serving police officer today who will not be saddened, shocked, and very troubled by what the Home Secretary has said, and the conclusions that Mr Ellison has reached.
He insisted that "corruption has no place in the Met Police":
A public inquiry into the operation of the SDS and undercover policing, whilst challenging because of its very nature, represents a real opportunity to provide the public with as complete a picture as possible of this unit, how it came to be and the hugely different policing context it operated within.
Corruption has no place in the Met Police - and people need to know that they cannot hide behind the veil of the past.
Former SDS officer Peter Francis said he was "delighted" by the news that a judge-led public inquiry will be held into the work of undercover police.
"I have been calling for such an inquiry since October 2011," he said.
"When the full truth comes out about the Police's work and activities, across the UK, against political campaigns and protests since 1968, I think they will be very shocked.”
A spokesperson for Boris Johnson, Mayor of London, said: "The Mayor's Office takes the findings of the independent Ellison Review very seriously and we intend to take the time to digest the report in full.
"The report contains profound and disturbing findings related to the Stephen Lawrence investigation and subsequent inquiries. All allegations must be investigated fully and those responsible held to account.
"We recognise the serious impact these findings could have on public confidence in the police, and it is essential we have a Met police that is trusted and respected by all Londoners."