A senior detective has revealed he decided that taking any action against Lord Brittan over a rape allegation would be "grossly disproportionate" more than a year before the peer died without knowing he had been cleared.
Detective Chief Inspector Paul Settle, of the Metropolitan Police, told the Commons Home Affairs Committee he decided the inquiry should not proceed in September 2013.
Lord Brittan, the former Conservative cabinet minister, died in January without being told he would not face action over a claim that he raped a 19-year-old woman known as "Jane" in 1967.
The investigation had been reopened last year and he was interviewed by police while seriously ill.
Mr Settle worked on the case after the complaint was made in 2012.
He told the committee: "On the 4th September 2013, following advice I received from the Crown Prosecution Service...regarding police applying what is known as the code test I decided that the investigation should not proceed any further.
"My reason for that was that I concluded that any action against Lord Brittan would be grossly disproportionate and would not have a legal basis as in order to interview him we would have to have had reasonable grounds to suspect that an (offence) had been committed.
"The investigation had shown that whilst an allegation had been made, the offence had not been made out in law and as such those reasonable grounds had ceased."