LONDON -- Sixteen years after the bloodiest terrorist bombing campaign in Britain's history, reverberations from those blasts can be felt again -- this time among those responsible for having arrested and convicted the alleged perpetrators.

At a time when Britain is again being shaken by a new wave of bombings that police believe are the work of the Irish Republican Army, the legal system is taking another look at the earlier cases. In those cases, some of Britain's most senior jurists and police officials stand accused of involvement in what author Robert Kee has called "the largest miscarriage of justice ever revealed in British history."

Critics are asking how such a major failure could have occurred and are pointing fingers not only at the officials involved, but at the criminal justice system itself.

Fresh evidence has revealed that police physically and mentally abused the Irish-born defendants, fabricated confessions in some of the cases and discarded or withheld alibi evidence in others. Laboratory test results were doctored in some cases, and those that might have exonerated some of the defendants were concealed. Judges also routinely quashed appeals, ignoring or denigrating new defense evidence that might have led to dismissals or acquittals.

It all happened, critics contend, because police, under enormous public pressure, set out to get convictions by any means necessary, and because judges refused to consider the possibility that government witnesses would lie.

"A prejudice against the Irish was part of it," said Chris Mullin, a member of Parliament, who has written a book about one of the cases. "But just as important was the idea that small lives can be thrown away in order to protect greater reputations."

Following a prolonged campaign by Kee, Mullin and other crusaders, 11 of those convicted for their purported roles in the bombings have been released from prison or are in the process of official exoneration. Six others remain behind bars, but the government is conducting a new investigation into their convictions, and many legal experts believe they too eventually will be set free.

All of these changes have occurred despite staunch opposition from Britain's senior judges, some of whom are themselves implicated in the scandal. Those jurists will not discuss the issue publicly, although privately several insist that the people they helped send to prison were guilty. One key figure, Lord Lane, chief judge of Britain's court of appeals, has reportedly threatened to resign in protest if the government approves a new legal appeal by the six remaining prisoners.

"I'm sorry to say there hasn't been as much soul-searching as there ought to be in the legal establishment," said Michael Zander, law professor at the London School of Economics. "I think judges, especially at the more senior levels, are very resistant to accepting the notion that serious mistakes were made."

Britain's legal system is generally more inclined toward the prosecution than its American counterpart, according to legal experts here. Its trials usually are speedier, and judges are given far more leeway in interpreting evidence and guiding jurors.

The courts here are also less likely to exclude evidence, even when obtained by improper means, and tend to give more weight to confessions than American courts do. The Prevention of Terrorism Act, adopted by an outraged Parliament during the 1974 bombing wave, allows police to hold suspects for up to seven days without charge and to deny them access to lawyers for up to 48 hours.

"We don't have a written constitution and we have a very limited appreciation of individual rights, in particular the rights of suspects in criminal proceedings," said Gareth Peirce, a London lawyer who has defended clients in all three of the major bombing cases. "At any stage in a criminal investigation, there's a temptation and an opportunity for those investigating to abandon the rule book. And the more horrendous the crime, the larger the temptation."

Few crimes were more horrendous than the 1974 pub bombings, which killed more than 40 people and maimed dozens of others. Shocked by the slaughter, the British public demanded swift justice -- and the police and courts delivered. By the end of that year, police had arrested three sets of alleged bombers and bomb makers. The groups were known as the Guildford Four, the Maguire Seven and the Birmingham Six. All were convicted, and the convictions were all upheld by appeals courts.

From the beginning, however, many outsiders had their doubts. The Guildford Four were convicted solely on the basis of their own confessions -- which all four later repudiated. To some observers, the four young, emotionally unstable drifters who dabbled in drug abuse and petty theft seemed a far cry from the dedicated men of the IRA, the nationalist group that organized and directed the bombing wave as part of its guerrilla war to end British control of Northern Ireland.

"We all knew our clients were not of the caliber to commit such an act," recalled Alastair Logan, one of the defense lawyers. One of the four, Patrick Armstrong, "couldn't stop shaking, and he shook from the first day I met him until the day of his appeal."

Logan said the police, the judge and the prosecutor were all at fault -- but he also blames the defense. "It was a failure on our part as well," he said. "We dealt with it in a gentlemanly way when, in fact, the gloves were off against us. They were shafting us and we let them do it."

For Logan, the moment of truth came two years later when, after a tip-off, he interviewed and obtained sworn statements from four imprisoned IRA members who described in great detail their own roles in the bombings and flatly denied any involvement by the Guildford Four. Logan said he naively believed the authorities would launch a new investigation once they saw the statements. When they refused, Logan said he finally realized that the judges and the police were effectively in collusion.

"When I heard {the final} judgment, so capable of distorting the truth, I knew it was no longer justice; it was a question of all hands to the pump," he recalled.

The Maguires too seemed unlikely terrorists. Patrick Maguire was a British army veteran and a dues-paying member of the Conservative Party. His son Vincent hoped to become a policeman. But police swooped down on their north London house after Patrick's wife Anne was accused by one of the Guildford Four of operating a bomb factory there.

Police found no explosives in the house and never linked the Maguires to any bombings. But six members of the family -- including two children -- and a neighbor were convicted of illegally possessing nitroglycerine after lab tests reportedly found traces of the explosive on their hands. Government scientists testified that the tests were foolproof.

At the end of the trial, however, a former government scientist disclosed an official document questioning the tests and directly contradicting the testimony of the prosecution witnesses. Yet Lord Donaldson, the presiding judge, who is now Britain's second-highest judicial official, did not allow the evidence to be heard. Instead, he himself informed the jury of the new document in his summation of the case, but dismissed it as insignificant.

So things stood, until two years ago when lawyer Peirce came across a pile of police documents marked "Not to be disclosed to the defense." Among them was a statement by a roommate upholding one defendant's alibi for the night of the Guildford bombings. A new independent police investigation uncovered further notes indicating that the allegedly spontaneous "confessions" of the four had been carefully drafted by Surrey police.

A new appeals court hearing quashed the convictions, but only with the greatest reluctance. Lord Lane, said Paul Hill, one of the defendants, looked as if he had been forced to eat "a scalded cat."

The collapse of the Guildford case compelled officials to reopen the Maguire convictions as well. After four weeks of public hearings, another appeals court judge, Sir John May, issued an interim report two weeks ago that faulted not only the forensic scientists, but also Lord Donaldson, prosecutor Sir Michael Havers -- later Britain's attorney general -- and the three-judge panel that heard the appeal.

The Birmingham Six have always contended that their confessions were coerced from them after beatings and abuse by police. Mug shots taken after their arrest show most of them with facial cuts and bruises. Police, however, insisted that the beatings were administered by prison officials after the suspects had confessed.

"The general feeling was everybody knew the police were lying about the violence, but genuinely believed they got the right people, and that's how they justified doing what they did," said member of Parliament Mullin, whose book says the six were victims of a police frame-up. "It's only when people began to realize that these maybe weren't the right ones that they started coming forward."

Despite new evidence from witnesses who claimed to have seen the police beatings, and a document that appeared to show that police had falsified the times and dates of interviews with the defendants, a three-judge panel upheld the conviction in 1988, with a swipe at the government. "As has happened before in references by the home secretary to this court," said Lord Lane, "the longer this hearing has gone on the more convinced this court has become that the verdict of the jury was correct."

Peirce has submitted fresh evidence to the Home Affairs office, which oversees police matters, and Mullin says both he and the authorities know the names of those who actually carried out the bombings. But Birmingham police insist that the convictions are sound.

Most experts agree there is less likelihood of such abuses recurring today. After 15 years of battling the IRA, police are more knowledgeable and skilled in detecting and prosecuting terrorist offenses and have far better intelligence networks. Revisions in the criminal evidence laws have increased some of the protections granted defendants.

Still, many critics, including retired jurists Lords Scarman and Devlin, are calling for a major overhaul in the legal system to provide a review system that is more receptive to defendants' appeals. Many people also want changes in the way expert testimony is treated, more scrutiny of police conduct and of alleged confessions and an opening of the selection process for judges to get a younger, more racially mixed and diverse judiciary.