Police have been criticised by an independent watchdog for a botched raid that led to the death of reggae star Smiley Culture, it was revealed on Tuesday.

The Metropolitan Police Service (MPS) claim that Smiley Culture, otherwise known as David Emmanuel, died after stabbing himself through the heart during a drugs raid at his Surrey home on 15 March 2011.

The Independent Police Complaints Commission (IPCC) conducted an investigation into Emmanuel's death. The summary of their final report – the coroner has asked that the full report is not made public or shared with Emmanuel's family – condemns the raid as significantly flawed and compels the MPS to overhaul the way they plan and execute future drug seizures.

But the commission also concluded there was no evidence to justify pursuing criminal charges against any of the four officers at Emmanuel's house when the singer, 48, is alleged to have killed himself.

"The investigation has found no evidence that a criminal offence may have been committed," IPCC commissioner Mike Franklin announced in a statement. "The investigation [also] found there were no individual failings which, for the purposes of the [Police (Conduct) Regulations 2008], amounted to misconduct.

"However, the IPCC investigation did raise concerns about several areas of the operation, which included operational planning and risk management," Franklin added. "A separate report detailing the learning identified by the IPCC investigation is being sent to the MPS so that they can consider its recommendations and respond to the IPCC with actions for implementing learning where required."

Merlin Emmanuel, the singer's nephew, said his family has reacted to the IPCC findings with "anger, resentment and resilience" and accused the watchdog of treating them with "contempt".

None of the officers involved in the death of Emmanuel was suspended, and the IPCC's decision to treat them as witnesses and not suspects mean they were never formally interviewed.

Emmanuel's family want to know why the four officers handcuffed him after his fatal injury, even though an independent pathologist's report stated that the stab wound would have caused "rapid collapse and death within a few minutes".

They also question why the officer at the time of Emmanuel's death refused a direct request by the IPCC's lead investigator to give a formal interview.

They will now launch a private prosecution against the officers involved in the tragedy.

"We firmly believe Smiley was murdered and that the IPCC have let us down and treated us miserably," said Merlin Emmanuel.

"They promised us a thorough investigation and that they would get to the bottom of what happened.But there are still so many unanswered questions – and the IPCC have now made sure that the officers who saw what happened are never going to be pressed to tell the truth about what happened that day," he said.

Their disappointment in the IPCC's investigation has caused Emmanuel's family to set up The Campaign for Justice: a 24-hour advice and support line for people whose loved ones have died in police custody.

"Our experience has led us to the sad and awful conclusion that not only will there continue to be deaths in police custody but that grieving families will not receive justice or empathy from the system as it currently operates," said Merlin Emmanuel.

The IPCC report has been sent to the official coroner to begin preparation for the inquest, which will be held with a jury.

The inquest, however, will not take place before the conclusion of the criminal trials to which Emmanuel was allegedly linked. These two trials are scheduled to be heard in early 2012. The IPCC intends to publish its investigation report when all proceedings are concluded.