Reports of police brutality in South Africa have soared by 313% in a decade, experts warn, yet only one in 100 cases against officers results in a conviction.

A series of high-profile cases, including the shooting of striking mineworkers at Marikana and the killing of a Mozambican taxi driver dragged behind a van‚ have left the reputation of the service in tatters. Cases of police brutality leapt from 416 during 2001-2002 to 1,722 cases by 2011-2012, the Institute for Security Studies' (ISS) annual crime conference in Johannesburg heard on Wednesday.

Gareth Newham, of the ISS's governance, crime and justice division, said a total of 11,880 criminal cases were opened with the Independent Police Investigative Directorate (IPID) during the five years to from 2011-12. But this resulted in just 2,576 prosecutions and 129 convictions ‚ meaning that only 1% of criminal cases opened against police officials ends in a conviction.

No police officer has yet been arrested in connection with the massacre of 34 workers at the Marikana platinum mine in August last year, even though workers injured in the incident are still facing criminal charges.

There were 720 deaths in police custody or as a result of police action in 2011/12, a slight drop. Of these, 22% of cases were referred to the national prosecuting authority because of some evidence of criminality, Newham said.

The number of police disciplinary hearings that ended in a dismissal decreased from 12.2% to 9.6% between 2009-10 and 2011-12, when more than a third ended with no sanction against the officer, and 2,049 cases were withdrawn or ended in a not guilty verdict.

"Police misconduct is met with impunity," Newham said. "The most likely outcome of a case against the police is no outcome." This undermines the morale and public trust in the many honest police officers who do their work professionally and within the rules, he added.

The public is also paying the price through taxes. Police are facing civil claims valued at more than 840m rand (£52m) in relation to assault, and 1.1bn rand (£68m) related to shooting incidents. Total claims against the police have doubled in the past two years to 14.8bn rand (£920m).

Newham highlighted figures showing that 1,448 police employees have convictions for serious crimes ranging from murder to rape and assault. "Why are convicted criminals allowed to continue to serve in the organisation responsible for law and order?" he asked.

The police budget increased 222% to 66.7bn rand (£4.15bn) over the 10 years from 2003/4 to 2013/14, Newham said. Police personnel increased by more than 50%, or 67,035 posts, during 2002/3 to 2011/12.

But this mass recruitment into the police, while understandable in the face of high crime, was poorly thought through by senior management and resulted in large numbers of police on streets who were poorly trained, managed and supported, he argued.

Mass police recruitment put pressure on selection, training, supervision, discipline and performance management, and resulted in an increase of police misconduct, brutality and corruption, Newham said.

"Throwing more money and people at the police is not the solution. We don't need more people in police uniforms – we need professional police officers who are better trained, motivated and managed," he said.

Low pay and morale, the daily risks in fighting violent crime and the recent "militarisation" of the police ‚ introducing army-style ranks and encouraging a "shoot to kill" policy‚ have all been blamed for South Africa's culture of police brutality.

Dr Johan Burger, a former officer now at the ISS, said: "You cannot only refer to 'bad apples' any more. The problem is far bigger than a few individuals. It's about the leadership in the police itself addressing systemic factors."