BBC News Online explains the major issues about custody deaths and the reasons why they sometimes turn out to be contentious.
What is a custody death?
Deaths in police custody include situations where the deceased was 'arrested or detained in charge of a constable or otherwise in the hands of the police' as defined by the Police and Criminal Evidence Act 1984.
Aside from people actually arrested or detained, fatalities in the following situations are also classed as 'custody deaths':
People actively seeking to evade arrest
People involved in police 'stop and search' operations
People detained under the Mental Health Act
How many are there?
Figures from the Home Office show that between 1 April 2002 and 31 March 2003 there were 104 custody deaths, compared to 70 the previous year.
The large increase is partly explained by the decision in 2002 to widen the definition of custody deaths. The figure now includes those killed in road accidents involving police officers - a total of 40 people in 2002/2003.
The highest number of custody deaths took place in the Metropolitan Police Force area where 17 people died, followed by the West Midlands with 11 deaths.
However, deaths in custody are a very small proportion of the total number of people arrested or detained by police officers each year.
Why are some deaths more contentious than others?
The high proportion of people of ethnic minority origin dying in police custody has attracted particular controversy in recent years.
In 1998 Home Office research found deaths of black people in custody were nearly 10 times more likely than the deaths of white people to be linked to the use of restraint or struggles with police officers.
Inquest, a campaign group, says that in 1994 ethnic minorities accounted for more than 22% of custody deaths at a time when ethnic minorities made up approximately 6% of the UK population.
However, by 2002 the figure had dropped back to 9% of custody fatalities, making ethnic minorities only slightly over-represented. But in 2002/2003 the proportion of ethnic minorities dying in custody rose sharply to 16% of the total.
The circumstances surrounding the deaths of some white people in custody have also been highly contentious - such as the shooting of Harry Stanley by armed police in 1999.
Officers believed he was carrying a concealed gun - but it turned out to be a table leg.
Who investigates custody deaths?
Since April 2004 the Independent Police Complaints Commission (IPCC) has been responsible for supervising most custody death investigations.
The IPCC took over from the Police Complaints Authority (PCA) which campaigners complained was effectively the police investigating themselves.
The IPCC is composed of 18 commissioners who are not police officers but who have full police powers while on duty.
They must be given access to police premises, documents and other evidence when requested. The IPCC will also be able to supervise police investigations where necessary.
How many result in inquest verdicts of 'unlawful killing'?
Very few. Of approximately 655 cases since 1990 just nine have resulted in inquest judgements of 'unlawful killing'.
Of inquests held into the 70 custody deaths during 2001/2002 none resulted in an inquest finding of unlawful killing. However, there were three such verdicts in the year to April 2003.
And in October 2003 an inquest jury returned a verdict of unlawful killing in the controversial case of Roger Sylvester, a black man who died in police custody in 1999.
How often are police officers disciplined or prosecuted?
Cases of custody deaths rarely result in disciplinary procedures against police officers even after an 'unlawful killing' finding at an inquest.
Even fewer officers face criminal charges and in recent years none of those who ended up in court have been convicted.
The last case to come to trial concerned the death of Christopher Alder who died in a police station in Hull.
Five officers were charged with manslaughter but in June 2002 the case against them collapsed and the judge ordered the jury to acquit them.