The daughter of a late British peer has been shot dead in the Philippines in what appears to be a vigilante-style gang hit in the country’s bloody crackdown on drugs.

Maria Aurora Moynihan, 45, was left in the street in the capital Manila on 10 September, police said. Her attackers propped up a cardboard sign against her body which said: “Drug pusher to the celebrities.”

Moynihan was the daughter of the 3rd Lord Moynihan, a British peer who fled to the Philippines in the late 1960s following fraud allegations. He ran several brothels and was allegedly active in drugs trafficking until 1991, when he died of a stroke.

A dual British-Filipino citizen, Maria Moynihan was also accused of involvement in the narcotics business. She had been on bail following charges of possession of illegal drugs in 2013.

“Witnesses told us they heard a series of gunshots, then saw a vehicle leaving the area. They did not see its licence plates,” Ch Insp Tito Jay Cuden told Agence France-Presse.

He said no arrests had been made. “She’s considered a drug personality,” he added.

The Philippines president, Rodrigo Duterte, has spent his first three months in office waging a campaign to kill all involved in the rampant drugs trade, causing outrage from rights groups and foreign governments.

More than 3,500 alleged drug dealers and addicts have been killed, about a third of them in police operations but the majority by armed vigilante militias. Duterte has publicly encouraged civilians to kill addicts and said he will not prosecute police for extrajudicial executions.

Moynihan’s sister, a famous film actor in the Philippines, said her family had one priority following the death.

“That is to protect her children from further pain and suffering so that they, and we as a family may take this time to grieve, mourn but most of all celebrate the life of this exceptional human being I will forever have the privilege of calling my sister,” Maritoni Fernandez said. A police investigation is ongoing.

Rodrigo Duterte is waging a campaign to kill everyone involved in the country’s drug trade. Photograph: Lean Daval Jr/Reuters

Local media aired footage of a vehicle stopping and opening its door on the deserted part of the street where the body was later found. The video was too grainy to determine exactly what happened.

Moynihan’s father was described in his Telegraph obituary as a “confidence trickster, brothel-keeper, drug-smuggler and police informer”.

He succeeded his father in 1965 as the Liberal whip in the House of Lords. But by the end of the 1960s, he was facing more than 50 charges including fraud and so fled to Spain and then the Philippines.

He remarried a Filipino belly dancer who ran a chain of massage parlours across Manila and became involved in the local narcotic trade, according to Australian police. He referred to the then president Ferdinand Marcos as “my drinking chum” and avoided arrest.

After being linked to a Sydney criminal syndicate known as the “Double Bay Mob”, which was importing heroin from Manila, the baron was persuaded to act as a police informant.

In 1988, he helped secure the arrest of Howard Marks, the cannabis trafficker whose autobiography, Mr Nice, became a best-selling book. Moynihan secretly recorded “drug dealing” conversations with Marks for the US Drug Enforcement Administration.

Educated in French literature in Paris, Maria Moynihan was arrested in 2013 for alleged possession of shabu, or crystal meth, the drug Duterte wants to rid the country of.

• This article was amended on 21 September 2016 to clarify that people killed in the crackdown are alleged, not necessarily proven, to be drug dealers and drug addicts.

