The grieving sister of a man brutally murdered in The Gambia has called on Foreign Secretary Boris Johnson to help get justice, three years after he was killed.

Father of four Jack Kenley, 52, was repeatedly stabbed in his own home by a teenager police believe was trying to burgle his house in August 2015.

Despite arresting a suspect at the scene, who admitted killing Jack, the court case against him still has not been heard.

The trial has been adjourned more than 40 times and has been beset by problems including police bungles and confusion over the alleged killer’s age. When he was arrested he said he was 18 – which meant he would be tried as an adult – but when he later got a lawyer he claimed he was 17.

The state prosecutor is now refusing to carry out a bone test on the boy to verify his age and the court is trying him as a child. In another blow police failed to carry out the proper procedure when arresting the suspect so his confession has been deemed inadmissible. The prosecutor is also refusing to appeal that ruling despite calls from the family and their lawyers to do so.

Now Jack’s sister Elaine Kellett, from Maidstone, is calling on Boris Johnson to step in to put pressure on the state prosecutor to appeal the boy’s age test and appeal the decision about the confession. She also wants him to ensure the trial progresses after three years of delays.

Elaine, 52, said: “My brother was stabbed to death in his own home yet we have been waiting three years for justice and there is no sign of that happening any time soon. After fighting for justice for this long and experiencing over 44 adjournments to my brother’s case I am calling on Boris Johnson to step in and help us. Jack was a British citizen but it feels like he has been forgotten and there is a very real chance that his killer could walk free.

“He admitted killing my brother, but that was deemed inadmissible, and he is suddenly considered a child despite saying that he was 18 to officers when he was arrested. It is a shambles and the state prosecutor seems unwilling to appeal either of those things. That is why I am begging Mr Johnson to look at the case and see if there is anything he can do to help.”

Jack, who was living in Bedfont, West London and has 13 grandchildren, was introduced to his Gambian wife Fatou, who is in her 30s, through friends and moved to be with her in 2009. Jack offered Fatou the chance to come to the UK but she wanted to remain in The Gambia. Elaine said she had never seen her brother as happy as when he met her.

She said: “They were both madly in love and Jack was happier than I have ever seen him. He questioned whether moving to The Gambia was the right thing to do but as far as I could see it was. She is funny, strong and he just really loved everything about her.”

Jack moved into Fatou’s uncle’s compound when he initially moved over before building his own home with three cottages to rent out while Fatou worked in The Gambian Navy. They were very happy.”

But in August 2015 Elaine received a call saying that Jack had been stabbed.

“Isatou, who is Fatou’s adopted daughter, called me and said my brother had been stabbed, was on his way to hospital. I was shocked but it was difficult to tell how serious it was over the phone. I started panicking as I didn’t know what to do. It is so far away. I finally received a call to say that Jack went into surgery six hours after he was stabbed.

“Two hours later we had a call to say he was out of surgery and that he was asking for a cigarette. As a result we all assumed he was going to be all right. The next thing I knew I was getting a call from Fatou to say that he had died. I dropped the phone as I was in such a state of shock. Moments before he passed away he said to send his love to me, our mum and our dad. Fatou was crying down the phone and I couldn’t say anything as I was so devastated.”

Police rushed to the scene after Jack’s body was found in his bed covered in blood. They discovered his alleged killed hiding behind a door who said he had gone into the house looking for money to steal. He then pointed out where the murder weapon was and confessed to killing Jack when he stirred form his sleep.

Elaine said she blames herself for her brother’s death as she texted him at around the time the burglar was in his room and may have woken Jack. She believe that him waking up spooked the killer and he stabbed him to death.

She said: “My brother liked sleeping in and I texted him about 11am Gambian time. I later found out that that was when he was murdered. I can’t help but think that my text message woke him up and then he saw the killer in his room, which resulted in him stabbing Jack to death. I could have been the reason that my brother lost his life and that thought haunts me.”

Magdalena Knez, a specialist travel lawyer from Slater and Gordon, which is representing Mr Kenley’s family, said: “Mr Kenley was brutally killed in his own home and his alleged killer caught at the scene with the murder weapon. Yet, three years on Mr Kenley’s family are still seeking answers about what happened and justice for his murder. We echo Mrs Kellett’s call for the Foreign Office to taking a more active role to get this case heard and achieve justice for the family.”