Michael Jackson’s death from a cardiac arrest was probably the result of drug abuse, said a family lawyer who claimed the star was addicted to painkilling medication.

Paramedics were called to Jackson’s Los Angeles home just after noon on Thursday. He was rushed to UCLA Medical Centre where doctors battled in vain for an hour to save his life. He was pronounced dead at 2.26pm, with family members at his bedside.

The night before his death he had been in rehearsals for his 50-date London comeback tour.

Brian Oxman, the family’s lawyer and long-time friend, said Jackson’s family had long been concerned about his use of prescription drugs and blamed “enablers” in his entourage for making the situation worse.

There were reports that the 50-year-old singer had been given a painkilling injection shortly before his death.

Mr Oxman likened Jackson’s demise to the drug-related death of Anna Nicole Smith, the former Playboy model, and said it came as no surprise to those close to the singer.

His family believed his reliance on painkillers had become “extensive” as he struggled with injuries during rehearsals.

“This is a case of abuse of medications,” Mr Oxman said. “This is not something which had been unexpected. Because of the medication that Michael was taking, his family had been trying for months and months and months to take care of Michael Jackson.

“The people who have surrounded him have been enabling him. If you think the case of Anna Nicole Smith was an abuse, it was nothing in comparison to what we have seen taking place in Michael Jackson’s life.”

Mr Oxman told CNN: “Michael had appeared at rehearsals a couple of time, he was very seriously trying to be able to do this. His use of medication had gotten in the way, his injuries which he had sustained performing – where he had broken a vertebrae and had broken his leg from a fall from the stage – had gotten in the way.

“I do not know the extent of the medications that he was taking, but the reports that we have been receiving in the family is that it was extensive and this is something which I feared and something which I warned about.

“I don’t know the cause of all this so I can’t tell you what the ultimate result of it is going to be, but I can tell you for sure when you warn people that this is what’s going to happen and then it happens, where there is smoke there is fire.”

Drug use can cause cardiac arrest and Jackson had a long-standing reliance on painkillers. There were reports that the singer was taking Demerol, a powerful medication similiar to morphine, and the opiate Dilaudid. Toxicology tests will be carried out on his body and an autopsy is likely to be undertaken today. His body was flown to the coroner’s office by helicopter.

News of Jackson’s death was confirmed by his brother, Jermaine, who gave a press conference at the hospital.

He said: “My brother, the legendary King of Pop, passed away on Thursday June 25 at 2.26pm. We believe he suffered a cardiac arrest at his home, however the cause of his death is unknown until the results of the autopsy are known. The personal physician who was with him at the time attempted to resuscitated him.”

Stars from the world of showbusiness and politics united in tribute to the star who revolutionised pop music with albums such as Thriller, but whose later years were tainted by allegations of child abuse.

Sir Paul McCartney, who dueted with Jackson in the early 1980s on Say Say Say, said : “It’s so sad and shocking. I feel privileged to have hung out and worked with Michael. He was a massively talented boy man with a gentle soul. His music will be remembered forever and my memories of our time together will be happy ones.”

Madonna said: “I can’t stop crying over the sad news. I’ve always admired Michael Jackson – the world has lost one of its greats but his music will live on forever.

“My heart goes out to his three children and other members of his family. God bless.”

Prime Minister Gordon Brown paid tribute to Jackson, saying: “This is very sad news for the millions of Michael Jackson fans in Britain and around the world.”

Britney Spears said: “I was so excited to see his show in London. We were going to be on tour in Europe at the same time and I was going to fly in to see him. He has been an inspiration throughout my entire life and I’m devastated he’s gone!”

The Rev Al Sharpton, the civil rights campaigner, described Jackson as a “historic figure”, saying: “Michael Jackson made culture accept a person of colour way before Tiger Woods, way before Oprah Winfrey, way before Barack Obama.”

He added: “Many ridiculed him. It’s amazing to see how many people are now praising him that wouldn’t go near him in the last several years, and condemnde him. In our last conversation a couple of months ago when I was teasing him I was coming to England to see him perform again, he talked about how many people had let him down. I told him it didn’t matter, he had never let the fans down. ”

Quincy Jones, the music producer who worked with Jackson on Thriller, said: “I am absolutely devastated at this tragic and unexpected news.”

Paying tribute to the singer’s “talent, grace, professionalism and dedication”, he added: “I’ve lost my little brother today, and part of my soul has gone with him.”

There was speculation that the pressure of his forthcoming London dates may have been too much for Jackson.

AEG Live, which organised the concerts at the O2 Arena in Greenwich, said Jackson had passed a lengthy physical exam in early 2009, but he last toured 12 years ago and looked markedly frail at the press conference to promote the shows.

Fears for his health emerged after he postponed the earliest dates, and his aides were forced to deny that he was fighting skin cancer.

Max Clifford, the publicist and friend of Jackson, said: “You wonder if the strain of getting fit for this major tour proved too much. In recent pictures he looked anything but healthy. He was always someone who seemed to find it difficult to cope with fame.”

Another friend of Jackson, the illusionist Uri Geller, said there had been no indication that the singer was in a frail condition.

“I really have no words. He was a young and terribly fit man and he was getting ready for performances in England. He was just fine, the last I heard.”

Jackson lived as a virtual recluse following his 2005 acquittal on charges including child molestation and kidnap.

He repeatedly denied undergoing cosmetic surgery, despite very visible changes to his face and skin tone, and was criticised for forcing his children to wear veils whenever they were in public.

Born in 1958, Jackson made his musical debut with four of his older brothers in the Jackson Five before embarking on a solo career.

His 1982 album Thriller – which included the hits Beat It, Billie Jean and Thriller – is still the best-selling album of all time, with more than 26 million copies sold. His lifetime sales tally is estimated at 750? million.

In 1994, he married Lisa Marie Presley, the 26-year-old daughter of Elvis Presley. The couple separated two years later and Jackson later married Debbie Rowe, a 37-year-old nurse he met while undergoing plastic surgery in 1997. They had two children, Prince Michael and Paris Michael Katherine, before divorcing in 1999.

Jackson had custody of the two children and of a third, Prince Michael II, whose mother’s name has never been made public.