An independent review overturned Ms Saunders’ original ruling that the former Labour peer should face no action over child abuse allegations because he is suffering from Alzheimer’s.
A trial of the facts, where a jury hears the evidence against an individual considered too ill for a full trial, is now expected to be held into the 22 offences allegedly committed in the 1960s, 1970s and 1980s.
Simon Danczuk, the Labour MP for Rochdale who has campaigned for the case to be heard in court, said that Ms Saunders was responsible for a “catalogue of errors”.
He said: “I think she should resign for a number of reasons. She has made a number of bad judgments and she is just not fit to do the job.
“She made mistakes on a case around FGM [female genital mutilation], serious errors in her attempt to prosecute journalists and now another serious error regarding the Lord Janner case.
“She ignored her advisers, took a long time to make the decision, then announced it when parliament was not sitting although there was significant public interest.”
Mr Danczuk added: “Most important of all, it was a serious mistake because she failed to understand both the mood of the public and the emotional distress she was causing to the alleged victims.
“We cannot have somebody leading the Crown Prosecution Service who is cold and dispassionate towards alleged victims.”
Peter Garsden, a solicitor representing nine of the alleged victims in the Janner case, said that his clients wanted to see Ms Saunders go.
“As far as my clients are concerned, to a man they have all said that they think that Alison Saunders should resign,” he said.
“Now that Lord Janner is going to be prosecuted, they are delighted, but they still take the view that Alison Saunders has been proved wrong and that they have been exposed to unnecessarily long suffering while they awaited the outcome of this review.”
However, Ms Saunders said she would not be standing down.
The 86-year-old peer’s family strongly denies claims he used his power as an MP for Leicester to abuse vulnerable young boys at a local children’s home.
The case has been listed for a first hearing at Westminster Magistrates’ Court on 7 August this year.
A judge will have to decide if Janner is fit to plead. If he is not, a jury will be asked to decide whether he committed the acts he is charged with.
The judge will also have to rule on whether the defendant should appear during the trial or can be excused on medical grounds.
A trial of the facts is not considered a trial as such because the defendant cannot put forward a defence. There is therefore no guilty verdict and the court cannot pass sentence.
All it can do is make a hospital order, a supervision order or an order for the defendant’s absolute discharge.
Specialist abuse lawyer Liz Dux, who represents many of Janner’s alleged victims for law firm Slater and Gordon, said her clients were “delighted” by yesterday’s announcement.