There were 17 fatalities in or following detention in the most recent financial year – six more than the previous 12 months, the Independent Police Complaints Commission said.
The last time the figure was higher was in 2010/11, when it stood at 21.
It was also revealed that there were 69 apparent suicides following custody. This is 50% higher than the 46 people in 2010/11.
Theresa May will launch a major review into deaths and serious incidents in police custody later.
The 17 deaths recorded in or after police custody in the last financial year is “broadly in line with the average” over the last six years, the IPCC said. Last year’s total of 11 was the lowest since recording began in 2004/5.
Fourteen of those who died were men and three were women. They were aged between 22 and 57. Fifteen were white, one was of Asian ethnicity and one was from a black background.
The report showed there were 69 apparent suicides following police custody in 2014/15 – one fewer than the previous year. Cases are included if they happen within two days of a person being released, or where the time spent in custody may have been a factor in the death.
Twenty-two occurred on the day of release from police custody, 33 occurred one day after release, and 14 occurred two days after release.
Data indicates that the number of people taking their own lives after being detained by police has risen sharply in the last three years. In 2011/12, the number was 39.
Eight of the 17 people who died in or after police custody and half of those who apparently killed themselves had mental health concerns.
Drugs and alcohol were also said to be a factor in a number of the deaths.
The report also said:
:: There was one fatal police shooting – the first in three years.
:: There were 14 road traffic fatalities, continuing a downward trend. Seven people died following “pursuit-related” incidents.
:: Investigations were carried out in to 41 other deaths following contact with the police in a wide range of circumstances, including 26 people who died after concerns were raised with the police about their safety or well-being.
IPCC chair Dame Anne Owers said: ” “One of the IPCC’s most important functions is to investigate deaths in or following police custody, to make sure that lessons are learned and future deaths prevented wherever possible.
“Regrettably, our investigations have too often exposed the same issues: inadequate risk assessments; token checks on a person in custody; insufficient handovers between custody staff; a failure to recognise or properly deal with people with mental health concerns or substance abuse issues; poor liaison between police and other agencies.”
Launching the new review later, Mrs May will criticise the “evasiveness and obstruction” that apparently faces bereaved families.
She is expected to warn that every death in custody “has the potential to undermine dramatically the relationship between the public and the police.”
Marcia Rigg-Samuel, whose brother Sean Rigg died at Brixton Police Station in 2008, said: “Families of those who have died in police custody have for too long been badly treated by state agents.
“There is a clear need for a radical overhaul of how the whole system works following a death in police custody, and I hope that the independent review will address this, as well as the root causes of these avoidable deaths and ensuring accountability for those who fail in their duties to members of the public.”
Ajibola Lewis, whose IT graduate son Olaseni Lewis died after he was restrained in a south-east London psychiatric hospital in August 2010, accused authorities of “deep-seated and repeated failures”.
She said: “If the review is going to be more than an exercise in public relations, and if it is to enjoy the confidence of families in our position, it must find a meaningful way to learn from and reflect our experiences. ”
The figures published by the IPCC cover England and Wales.