Kenneth Clarke is undermining work in bringing rapists to justice by returning to the "bad old days" when the offence was treated less seriously, Labour's deputy leader, Harriet Harman, will warn on Monday.
As the justice secretary prepares to face MPs, Harman says Clarke struck a "raw nerve" when he appeared to suggest some rapes were more serious than others.
In an open letter to Clarke, to be published on the Guardian's Comment is free site, Harman says the criminal justice system has made great advances in the past decade which has meant victims of rape are treated in a much more sensitive way.
Harman writes: "Your job is to lead the criminal justice system and to continue the improvement in bringing rapists to justice....But your comments last week were an echo from the bad old days. You should support, not undermine the extraordinary and dedicated work of bringing rapists to justice. You should be protecting rape crisis centres, supporting sexual assault referral centres, praising the pioneering work of the crown prosecutors and protecting the police from cuts which will hit their painstaking work on rape.
"You believe that people who get it wrong can turn over a new leaf. That is what you need to do."
Clarke will face MPs for the first time since his remarks last week in which he rejected a suggestion that "rape is rape". He later apologised. "I got bogged down in a silly exchange," he said on Question Time, adding that he had been attempting to point out that the law takes account of the different circumstances of each rape case.
He will face questions from Labour on his plans to decrease sentences by up to 50% for early guilty pleas.
