NHS medical blunders dating back more than two decades are still costing millions of pounds a year in compensation, it has emerged.
The negligence bill for mistakes made before 1995 – mainly maternity failings – has begun to rise for the first time in five years.
A patients' charity said the figures showed just how long some families have to wait for payouts.
The NHS said it had taken steps to speed up the process.
'You can't tell how affected they are going to be'
Medical mistakes left youngster Thomas Hord, now eight years old, with cerebral palsy affecting all four limbs. He is unable to speak or walk.
Thomas was starved of oxygen at birth after midwives failed to place a foetal heart rate monitor in the right position.
But although Surrey and Sussex Healthcare NHS Trust quickly admitted mistakes had been made shortly after his birth in 2009, the family had to wait a further seven years for compensation.
They secured a £2.5m lump sum and will also get annual payments for Thomas's care.
Thomas's father Chris, 44, of Crawley, West Sussex, said it can take lawyers years to work out the extent of the damage to a child.
"A lot of it is to do with the fact you can't tell how affected they are going to be until a child starts going through their development," he said.
The bill for medical negligence claims in England has risen four-fold in the past decade, to £1.6 billion last year.
But the NHS in England also has a separate Government-funded scheme to deal with negligence claims for events before April 1995.
Its payouts rose by 13% last year to £27.7m, the BBC's analysis of official data shows. It is thought increased life expectancy and rising care costs may be behind the rise.
Patients' charity Action Against Medical Accidents said the growing size of the historical bill demonstrated the tragic, long-term human cost of often basic maternity errors.
Chief executive Peter Walsh said: "We, as a charity, have been going for 35 years and we still see the same mistakes, the same avoidable errors causing injury now as we did 35 years ago."
Mr Walsh called for more consistency in NHS training for midwives and doctors, saying examples of good practice seen in some hospitals should be rolled out across the country.
'There is an element of post-traumatic stress'
Sixteen-year-old Daniel Spencer, from Malvern, Worcestershire, was left severely disabled after being starved of oxygen shortly before birth.
Daniel requires round-the-clock care, uses a wheelchair and struggles to communicate, after failings in care during labour at Worcestershire Royal Hospital in 2001 left him with cerebral palsy.
His family's fight for justice took nearly 14 years.
Father Olly said it took 12 years for the NHS trust to admit partial liability for his son's condition.
The family had to fund Daniel's care themselves during that time, with mum Susan giving up work to look after him.
He said: "Any parent who has gone through what we have been through knows there is an element of post-traumatic stress.
"I have had lots of sleepless nights from it and a lot of things like money worries, while we try and fight the case and try and deal with everyday life."
In 2015, the courts awarded Daniel a £2.7m lump sum, with extra annual payments for ongoing care.
At the time, Worcestershire Acute Hospitals NHS Trust said it "sincerely regrets" the injury Daniel suffered.
The money is now helping to pay for specialist equipment, which Olly said was often "stupidly expensive", as well as home alterations and physiotherapy.
Why do families wait so long for compensation?
There are a number of reasons why many years might elapse between a medical mistake and a negligence payout.
Complex legal cases can take a long time to resolve and often involve extensive medical assessments.
Sometimes, assessments about a child's care needs can only be made when they are older.
In other cases, families don't realise until years later that they might have a claim.
Critics also say that too often the NHS refuses to admit responsibility, meaning the court process takes longer and costs more.
Mr Walsh said: "We have seen claims that have taken over 10 years to resolve.
"Things have improved, but not enough has been done to speed up the process."
NHS Resolution, which handles negligence claims on behalf of English hospitals, said it was still receiving new claims under the historical scheme.
A spokesman said the cost of those claims was also rising because of factors such as increasing life expectancy and a recent change to the way lump-sum payments were calculated.
He said: "NHS Resolution is now involved right from the start in order to improve the support for families and the healthcare staff involved in these rare but tragic incidents and to speed up resolution."
From next year, NHS Resolution will also offer cash incentives to hospital trusts which take steps to make maternity services safer.
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It forms part of a Government plan to halve the rate of neonatal deaths, stillbirths, maternal deaths and brain injuries caused during or shortly after labour by 2025.
The Department of Health, which foots the historical negligence bill, said the plan would "help to reduce traumatic and costly safety failings in the NHS".
'Excessive legal costs'
Legal costs made up more than a third of the overall NHS negligence bill in the past five years.
The Department of Health has set out plans to cap the fees that lawyers can recoup from the taxpayer when they win negligence cases for their clients.
A spokesman said: "We're ensuring taxpayers' money is spent effectively by taking action against law firms creaming off excessive legal costs that dwarf the damages recovered – but we're also clear we want to ensure patients continue to access justice at a reasonable cost."
But Mr Walsh said this plan "risks denying access to justice and the opportunity for the NHS to learn much-needed lessons".
The hospital trust responsible for the biggest historical negligence bill, at £8.4 million over the past five years, was Bradford Teaching Hospitals NHS Foundation Trust. The trust declined to comment.
The trust with the second-largest bill, Doncaster and Bassetlaw Hospitals NHS Foundation Trust, said its historical negligence costs had dropped by nearly half since 2013/14, reflecting its "improvement journey".
Third-place University Hospitals Bristol NHS Foundation Trust said its historical negligence bill related to 12 cases dating back to before 1995.
A spokesman said: "Nine of those relate to children who underwent heart surgery at the Bristol Royal Infirmary in the 1990s, prior to the public inquiry, which resulted in wide-scale changes in clinical governance across the NHS."
In general, trusts which run larger hospitals would be expected to have larger historical negligence bills.
Across the UK
Payouts for historical negligence cases in Northern Ireland nearly trebled last year, to £4.1m.
A spokesman for Northern Ireland's Department of Health said most of this cost related to just two cases.
Historical cases – defined as those before 1993 in Northern Ireland – accounted for 15% of its entire litigation bill over the past three years, a much higher proportion than in England.
The NHS in Scotland has no separate scheme for historical negligence cases, but around £4.5m was paid out last year for mistakes made before 1998.
However, the proportion of claims arising from mistakes in maternity wards has halved in the past decade.
The Scottish Government said its NHS had a commitment to "learning lessons when something goes wrong".
In Wales, health trusts paid more than £160,000 last year for medical mistakes made more than 20 years ago, although not all trusts responded to requests for information.
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The Shared Data Unit makes data journalism available to news organisations across the media industry, as part of a partnership between the BBC and the News Media Association. This piece of content was produced by local newspaper journalists working alongside BBC staff.