On an appeal against sentence, the sentence may be decreased but not increased, except that one part may be increased to compensate for a reduction elsewhere. Time spent in prison on remand or awaiting appeal is normally counted against the sentence, but the Court of Appeal has the power to date sentence from its own decision and so discourage frivolous appeals.
When an appeal is allowed (and no new trial is ordered), the conviction is no longer regarded as such, and the sentence is clearly annulled. However, this does not of itself give the defendant any rights to compensation for time he has already spent in custody, and unlawful breaches of a court order are still punishable even though that order may cease to have future effect.
In R v Thames Magistrates Court ex p Levy (1997), a man D convicted of several motoring offences was barred from driving for a year. He appealed against the conviction and the appeal was granted, but in the intervening months he had been stopped two times and charged with driving while disqualified. D's application for judicial review of the court's decision that he should be convicted on that further charge was unsuccessful. Simon Brown LJ said D was guilty once and for all when (pending an appeal) he nevertheless drove a motor vehicle while an order of disqualification was lawfully in force.
The prosecution cannot appeal against an acquittal, though it can (like the defence) appeal against the judge's ruling on a point of law at a preparatory hearing before the jury is empanelled. Under the Criminal Justice Act 2003 the prosecution can also appeal against a "terminating ruling" made by the judge during the course of the trial, or against any other ruling (such as the exclusion of important evidence) that significantly weakens the prosecution's case, before the case is finally entrusted to the jury. Such an appeal must be lodged almost immediately, and the trial is adjourned while the Court of Appeal considers the matter.
The prosecution cannot formally appeal against the sentence, but the Attorney-General can refer an "excessively lenient" sentence to the Court of Appeal. The Court studies the transcript and hears legal argument; it may then increase (or reduce) the sentence.
The Attorney-General can also refer a point of law to the Court of Appeal: the Court hears legal argument and rules on the point of law. This sets a precedent for future cases, but does not affect the instant case. Either side can then appeal (with leave) to the House of Lords on a point of law of general public importance.
In two exceptional situations, a person can be retried (in front of a new jury) after he has been acquitted. The Criminal Procedure and Investigations Act 1996 allows a High Court judge to order a new trial where someone has subsequently been convicted of interfering with a juror or witness at the original trial, and the Criminal Justice Act 2003 allows the Court of Appeal to order a new trial where "new and compelling evidence" has come to light.
Miscarriages of justice may take place because mistakes can and do happen. It has often happened that innocent people have been convicted and the guilty are acquitted. It is inevitable but Blackstone said it is better that ten guilty men should go free than one innocent be convicted. There is an appeal system so that some of the wrongful convictions can be put right, but there are serious doubts about its effectiveness.
For example, Timothy Evans was hanged in 1950 after being convicted of murder; the real murderer was identified shortly afterwards, and Evans was pardoned (posthumously) in 1966. John Taylor's 1962 conviction for burglary was quashed, in respect of which he had long before completed a five-year prison sentence. In all these cases, the defendants' original appeals had been rejected.
The Criminal Appeals Act 1995 tried to rectify some of the shortcomings of the system: under s.2(1) of this Act the Court of Appeal should allow an appeal if it thinks the conviction is "unsafe", regardless of technicalities. In the past, however, the Court of Appeal have been very reluctant to interfere with the jury's verdict: the jury have seen the witnesses' behaviour in the witness box, and twelve jurors are as good as three judges in deciding who is telling the truth.
From 1968 to 1997 the Home Secretary had power to refer any case back to the Court of Appeal for further consideration. This was not particularly successful, because the Home Secretary as a politician didn't want to be seen as soft on crime, and the Court of Appeal were still reluctant to overturn a jury's verdict unless there was powerful new evidence.
In April 1997, a Criminal Cases Review Commission took over the Home Secretary's responsibility for investigating alleged miscarriages of justice and referring them back to the Court of Appeal where it thinks it appropriate. (It may also refer a conviction in the magistrates' court to the Crown Court, as if it were an appeal there.) The Commission has a staff of about 60 - three times as many as dealt with appeals in the Home Office under the old system - but detailed investigative work is still done by the police.
The Birmingham Six case is a clear example of a miscarriage of justice, but it is not easy to see how the judicial process could have prevented its occurring. It emerged fifteen years after the conviction that the scientific evidence of recent contact with nitroglycerine might have come from traces of ordinary soap, and (more significantly) that police officers had deliberately lied on oath and/or falsified interview records, these having been "absolutely critical" evidence at the trial.