Fifty-eight unexplained drug deaths involving GHB, the drug that was used by serial killer Stephen Port on his victims, will be investigated by the Metropolitan Police.

The Met came under fire following the conviction of Port and have been hit by accusations that they missed signs that linked the deaths of the four young men.

The 41-year-old chef drugged and murdered four young men, including victims from Lewisham and Gravesend, and raped several others he had lured to his flat after meeting them via web dating services.

The Met will now investigate 58 GHB deaths across the capital over the last four years to make sure that foul play has not been missed.

At least two lives could have been saved if police had not "brushed off" concerns of victims' loved ones and recognised foul play sooner, according to campaigner Peter Tatchell.

He said: "If four young well-off women had been murdered in Mayfair, I believe the police would have made a public appeal much sooner and mounted a far more comprehensive investigation.

"The killing of low income gay men in working-class Barking was treated very differently. Police officers stand accused of class, gender and sexuality bias."

The Met appeal in late 2015 was a year too late and if police had acted sooner two young men might still be alive, he said.

"It is appalling that the police did not alert the gay community in the autumn of 2014, after the third murder, that a serial killer could be on the loose."

The human rights campaigner said the police "mishandling" echoed failings in the serial killer cases of Dennis Nilson, Michael Lupo and Colin Ireland, showing lessons had not been learned.

Officers allegedly dismissed the possibility that four Barking GHB overdose deaths in almost identical circumstances might be suspicious.

Action was only taken after the family of Port's fourth victim, Jack Taylor, demanded answers on learning that all the men had their mobile phones taken, it is claimed.

Mr Taylor's family, who are planning to sue, said: "We do believe Jack would still be here if they had done their job.

"The police should be held accountable for Jack's death. We do understand it's not them who took Jack's life, but Stephen Port would have been stopped."

The family refused to accept Mr Taylor would have taken drugs willingly and put pressure on officers to treat his death as suspicious.

An Independent Police Complaints Commission inquiry is ongoing into the handling of the case and 17 officers are facing investigation into possible misconduct.