The NHS is suing seven drug companies claiming they colluded to fix the price of common prescription medicines.
Generic medicines account for two out of every three NHS prescriptions
It alleges that the NHS was forced to pay over the odds for these drugs and is seeking £30m compensation.
However, the claims have been strenuously denied by the companies, which have vowed to fight the case.
The case is part of a massive investigation into alleged price fixing, which the NHS says may lead to further court action.
The firms being sued though the High Court in London are Norton Healthcare Ltd UK, Norton Pharmaceuticals, Regent-GM, Kent Pharmaceuticals, Generics UK, Ranbaxy UK and DDSA Pharmaceuticals.
The companies all make generic medicines by copying formulas no longer protected by patent laws, which account for two out of every three NHS prescriptions.
The companies say strong competition between them has resulted in the lowest prices in Europe.
The Serious Fraud Office is also investigating allegations of drug pricing fraud, but the NHS says its action is being taken independently.
The organisation pursuing the claim for the NHS is its Counter Fraud and Security Management Service, led by chief executive Jim Gee.
He said all the civil claims being brought "will be vigorously pursued to secure the maximum possible recovery for the NHS either by judgment and damages or earlier agreement with the defendant companies".
He said investigations into the anti-competitive supply of over 30 other generic drugs were continuing.
"Nobody should be in any doubt about the NHS's determination to defend itself against unlawful behaviour and to ensure that its resources are protected and spent on the best possible patient care," Mr Gee added.
The companies being sued by the NHS have strenuously denied claims they colluded to fix the price of drugs.
They have also vowed to vigorously defend themselves when the case comes to court.
A spokesman for Ranbaxy UK said: "We do not believe that we have behaved in an improper way and will defend the legal proceedings vigorously."