Former home secretary Leon Brittan should have been informed before he died that a rape allegation against him had been dropped, one of the UK's most senior police officers has said.
Scotland Yard Deputy Assistant Commissioner Steve Rodhouse wrote to Lord Brittan's widow to apologise for failing to tell the family the peer had been cleared and that no further action was to be taken, The Times said.
Lord Brittan died of cancer earlier this year, but was unaware that police had decided there was no case for him to answer over allegations that he raped a 19-year-old student in 1967.
The Crown Prosecution Service found in July 2013 that there was not enough evidence for a prosecution, but the decision was never passed on to the peer.
The case was reopened last year after MP Tom Watson wrote to the Director of Public Prosecutions and Lord Brittan was interviewed under caution, when he was seriously ill.
Allegations again fell through but his family were again not told.
The Times said Mr Rodhouse has written to Lady Brittan's lawyers, Mishcon de Reya, saying: "I do recognise that this clarity should have been provided at an earlier stage and I apologise for any distress that this has caused to Lady Brittan."
The apology from Scotland Yard comes after a BBC Panorama investigation into allegations about a so-called Westminster paedophile ring, which is said to have murdered three boys in the 1970s and 1980s.
The programme featured a man, known only as David, saying he might have been led into making the claims by campaigners. David said he had provided the names of VIPs, including Lord Brittan, "as a joke suggestion to start with", but that he later repeated them.
The Met said it had "serious concerns" about the impact of the programme on Operation Midland - its investigation into historical child sex abuse and murder - and any effect it might have on witnesses and the willingness of victims to come forward.
On Wednesday it emerged that the Royal Family and other establishment figures offered their support to a senior clergyman who was accused of sexual offences more than two decades ago, though they may not have known the full facts.
Peter Ball was jailed for 32 months at the Old Bailey for sexually abusing aspiring priests, 22 years after allegations first came to light. Ball - once the Bishop of Gloucester - and former Archbishop of Canterbury Lord Carey had been assured in 1993 that there would be no future action against him, but a judge refused to dismiss the case.
Asked if the Prince of Wales had ever written a letter in support of Ball, a spokeswoman said: "The Prince of Wales made no intervention in the judicial process on behalf of Peter Ball."