Relatives of three young men who were killed by Stephen Port are suing the police force for failures in the investigation.

Daniel Whitworth, from Gravesend, was murdered by Port, along with Anthony Walgate, Jack Taylor and Gabriel Kovari.

The chef drugged his victims with GHB - known as 'liquid ecstasy' - so he could carry out his sick fantasies of having sex with their unconscious bodies.

Last month, the 41-year-old, from east London, was handed a whole life term for the murders, as well as raping four other men.

Now, Mr Whitworth's stepmother Amanda Pearson has joined forces with Mr Walgate's mother Sarah Sak and Mr Taylor's sisters Donna and Jenny Taylor to launch legal action against the Met Police.

It was the families who forced the police to look at a potential link between the killings, after they were initially put down to overdoses and in Mr Whitworth's case, a suicide.

Port left a sham suicide note on Mr Whitworth's body, in which he apparently confessed to the killing. But the Met did not check the handwriting on the note to check it if it was really written by Mr Whitworth.

An investigation by the Independent Police Complaints Commission into the handling of the four deaths is looking at whether three of the victims could have been saved if the warning signs had been spotted in the first victim, Mr Walgate.

The victims' families believe they could have, and 17 officers are being examined over their role in the case.

While the four women were being interviewed on the Victoria Derbyshire programme, Ms Pearson said: "They [Met] didn’t see it as suspicious; it was a while before we saw it [the note] anyway. We couldn’t understand why he would do that.

"I know people who do actually commit suicide are very good at covering up things but the content of the letter said he’s accidentally taken the life of Gabriel and we’d been out to family functions and things since that time, since Gabriel was found, and we truly couldn’t believe how he would be functioning, with that knowledge, as well as he was. It didn’t make sense.

"The note also said police should ‘blame the man I was with last night’ [Port] but when we asked 'where has he been, who was the man he was with last night?', “We don’t know, we may never know” was the reply we got.

"We did trust the [Met], even in their absence, to be doing something. We were finding the whole circumstance pretty difficult to deal with.

"His grandma especially, they were very close. We had yet to give that news to her, try and explain it to her.

"This lady has already lost a son to suicide, and then she lost her only grandchild to what we thought was suicide.

“He was a very happy man, with his job and his life in general."

A chef and former Dartford Grammar School pupil, Mr Whitworth was described as not being a party boy, or into using drugs.

Ms Pearson continued: "He wasn’t out there doing that kind of thing. He worked unbelievable hours. His recreational time was minimal and when he did go out he went out with his partner. But the police didn’t want to know about his personality really, they’d made up their minds.

“The police were very difficult to get hold of. Our liaison officer didn’t liaise.”

In Sarah Sak's case it took nine month for a liaison officer to even visit them.

Mr Whitworth's family were also expected to accept that their son had in fact killed Mr Kovari, and was a murderer himself.

Ms Pearson added: “I remember saying, 'I wish he’d have come to us'. It would have been misadventure, of course it would have been accidental, our son isn’t a murderer.

“All the time we were trying to fathom how he kept that to himself.

“His partner was trying to work out how he could have even been in the Barking area when Gabriel died.

“Had I known those things, I know I would have not stood back. So many things were coming to light in Walthamstow coroner’s court.”

In the case of Anthony Walgate, he was found with his underwear on inside out and back to front, wearing somebody else's t-shirt four sizes too large for him, but no questions were asked by officers.

Ms Sak said in the interview: "We were told time and time again 'nothing to investigate, there were two people in that room, one’s dead, so you’ll never know the truth'.

"It was so hard to get any information and they just refused to investigate it. They were appalling.

"A child could have put together the clues he [Port] was giving out."

In the case of Jack Taylor, the syringes and drugs bottle left on him were not checked or tested by police either.

His sister Donna Taylor said: "We just knew [Jack] didn’t die of a drugs overdose, we just knew we had to get them [Met] to listen to us and try and piece it all together.

"We needed them to look at the whole situation. We did a lot of our own homework on it. There were so many similarities which linked the [deaths].

"Stephen Port took Jack's life, but the police who didn’t do their jobs with any of the families, as far as we’re concerned, have played a massive part in Jack’s death.

"If they’d done their jobs properly, Jack would be here today. There is no other way of looking at that. We want them to be held accountable.”

The Met’s commander in charge of the specialist crime and operations command has written to each of the families to apologise for missed opportunities and express condolences but the women all agreed it was too little too late.

Donna added: "A letter when somebody's life’s been taken who is so dear to you, doesn’t cut it.”