The NHS may have to pay up to £3.5m in damages to prisoners who claim they received poor support in giving up drugs.
As many as 1,000 prisoners are claiming clinical negligence and a breach of human rights.
The legal action is based on claims that inmates were forced to go on detoxification programmes but were not given methadone.
In total, 55 primary care trusts and care trusts are aware of claims made against them, while a further 14 are yet to be notified.
This relates to around 400 claims, involving £3,500 each in potential damages, but solicitors believe this could rise to 1,000.
Healthcare law specialist Hempsons is acting for the NHS Litigation Authority. Partner Julie Austin said: “PCTs need to be reviewing their policies and procedures, making sure they meet the current acceptable standards of best practice.”
A preliminary hearing at the Royal Courts of Justice will take place in late summer.