Labour has suspended Lord Janner from the party after prosecutors said he would have faced trial over child abuse allegations if he wasn't suffering from dementia.
A Labour spokesperson said: "In the light of these very serious allegations, Lord Janner has been suspended from the Labour party."
The Crown Prosecution Service said that after a two-year investigation, 86-year-old Greville Janner would not stand trial because of the "severity" of his dementia.
But they said the allegations were "extremely serious" and "it would undoubtedly have been in the public interest to prosecute" if he were well enough.
The former MP for Leicester West is alleged to have preyed on boys at local children's homes in the 1970s and 1980s. Janner told parliament in 1991 that there was "not a shred of truth" in the claims.
Labour politician Simon Danczuk, who is standing for re-election in Rochdale, called on the director of public prosecutions, Alison Saunders, to make the evidence public.
He told BuzzFeed News he was "disappointed" with her decision not to prosecute.
"In light of the extraordinary circumstances surrounding this case, I will be writing to Alison Saunders asking her to make the evidence gathered public with appropriate redactions to protect victims and witnesses," he said.
"I remain very much of the view that a man's age and ill-health cannot be weighted against a nationwide inquiry into an establishment cover-up. I am pleased that the Labour party has suspended Lord Janner. I wrote to the party some months ago suggesting this action and I'm glad it's now been taken."
Leicestershire police said the decision was "the wrong one" and sent the wrong message to abuse victims.
In a statement, assistant chief constable Roger Bannister said:
There is credible evidence that this man carried out some of the most serious sexual crimes imaginable over three decades against children who were highly vulnerable and the majority of whom were in care.
I am extremely worried about the impact the decision not to prosecute him will have on those people, and more widely I am worried about the message this decision sends out to others, both past and present, who have suffered and are suffering sexual abuse.
Labour politician John Mann also hit out at prosecutors over the decision.
Totally unacceptable decision by CPS in Janner case
If an MP or former MP is accused, with clear evidence, of child abuse, it is always, without exception, in the public interest to prosecute
In a statement, Janner's family said:
Lord Janner is a man of great integrity and high repute with a long and unblemished record of public service. He is entirely innocent of any wrongdoing.
As the Crown Prosecution Service indicated today, this decision does not mean or imply that any of the allegations that have been made are established or that Lord Janner is guilty of any offence.