A BBC investigation has learned that police were called by a mystery man who said Lord Lucan was shot and buried in the grounds of a Sussex manor house.
The body of Lord Lucan has never been found
The peer vanished in November 1974 after the murdered body of his nanny was found at his home in London.
Under the Freedom of Information Act, the BBC Inside Out show found the man had called several times in 1998.
He told police Lord Lucan was shot in the gardens of Grants Hill House in Uckfield and his body buried there.
After Sandra Rivett's death, Lord Lucan is believed to have driven to Uckfield to the house of his friends Ian and Susan Maxwell-Scott.
His blood-soaked car was later found in Newhaven, leading many to believe he had drowned in the Channel or fled.
He was officially declared dead by the High Court in 1999.
The Inside Out programme said the caller claimed to have been in the grounds of Grants Hill House on 7 November and saw three men walk out.
The cesspit has now been covered over by a bowling green
He heard a shot and claims the aristocrat's body was buried in cesspit in the grounds.
In a statement the police said: "The Metropolitan Police are aware of this allegation but do not consider it to be a strong line of inquiry.
"The Lucan case is currently under review and will be for some months."
Derek Wilkinson was the Sussex Police detective in charge in Newhaven on the night Lord Lucan vanished.
Property not searched
He said: "I know from my own memory - even though it was 30 years ago - there were only three passengers in the foot hall.
"There was a man and woman who looked to be husband and wife and there was another man.
The man produced a French card, and Mr Wilkinson said: "I am quite aware from the photographs that Lord Lucan was not the person who went past me."
Another retired officer, Roy Blackmore told the programme he saw Lord Lucan's car drive through Uckfield six hours about Mrs Maxwell-Scott said he had left her house.
Mr Blackmore was also sent to Grants Hill House but the property and grounds were not searched.
In October 2004, the police announced the investigation into Lord Lucan's disappearance would be re-opened.
Grants Hill House is now sheltered accommodation and the cesspit a bowling green.