The first case, that of Ernest Saunders, is to be heard next month. The former Guinness chairman was convicted of false accounting and theft for his part in the illegal multi-million pound operation to prop up Guinness shares while the company battled for control of the drinks company Distillers.
His case is that he was denied a fair trial, in breach of Article 6 of the European Convention on Human Rights, because he was compelled to incriminate himself under the powers of earlier criminal justice legislation - the Act of 1987.
These provisions are different to those in the 1994 Act, under which there is no threat of imprisonment or contempt of court charges for failure to answer questions. But, says John Wadham, of the civil rights organisation Liberty, the judges at the European Court of Human Rights may lay down principles forcing the Government to revoke the 1987 Act, or indeed the 1994 legislation.
The second case is that of John Murray, of Northern Ireland, due to be heard by the European Court of Human Rights on 20 June. Four years ago, Mr Murray was convicted of kidnapping by a Diplock court, in which a judge, sitting without a jury, pronounces on guilt or innocence. Mr Murray had remained silent when interviewed by police and during his trial. The judge, the Lord Chief Justice of Northern Ireland, drew "adverse inference" from his silence, using the provisions of the 1988 Criminal Evidence (Northern Ireland) Order, the model followed by the Government for the relevant sections of the 1994 Criminal Justice Act.
Mr Murray took his case to the European Commission on Human Rights, which, while it ruled against him on the adverse inference point, signalled that a different ruling may have emerged if he had been tried by jury. Nicolas Bratza QC, the member of the commission appointed by the British government, said: "When it is a jury which must decide, without giving reasons, what adverse inferences, if any, to draw against an accused from his silence and what weight to attach to such inferences in arriving at a verdict, the risk of unfairness occurring appears to me to be substantially increased, however carefully formulated a judge's direction to the jury might be."
While there were widespread demonstrations against the introduction of the 1994 Criminal Justice Act, the abolition of the right of silence, in particular, was strongly opposed by lawyers, pressure groups and two Royal Commissions.
Abolition reverses the age-old presumption of innocence until guilt is proved, thus shifting the burden of proof from the prosecutions to the defendant. It may also, it is argued, lead to more miscarriages of justice.
"Police pressure can produce false confessions and unsafe convictions, and the right to remain silent is a valuable safeguard against this," says Liberty.
False confessions lie at the heart of high-profile miscarriages of justice, notably the cases of the Birmingham Six, the Guildford Four and Stefan Kiszko.
Judith Ward's is another case in point. She had a history of mental instability, and workers in the field of mental health say that the abolition of the right to remain silent has grave implications for the vulnerable, who may admit to crimes out of fear or lack of understanding. The vulnerable may also include those in a temporarily emotional and confused state of mind.
Another argument for the retention of the right to remain silent is that the right to a fair trial and the presumption of innocence are upheld by international human rights laws. In July, the United Nations Human Rights Committee is due to examine the UK's human rights record. The committee works under the International Covenant on Civil and Political Rights, which sets out the same rights as those in the European Convention on Human Rights, as well as stating that a person is entitled "not to be compelled to testify against himself or to confess guilt".
The most vocal supporters of abolition include the police, who say that controls on questioning introduced under the Police and Criminal Evidence Act have made obtaining confessions much harder. (Although John Alderson, the former chief constable of Devon and Cornwall, has said that the Criminal Justice Act provisions will allow police to "exert legal and psychological pressure on individuals held in the loneliness of their cells".)
Others say that removing the right of silence will lead to a reduction in crime, since only the guilty hide behind silence. But according to Liberty, there is no evidence that silence is used mainly by professionals, or that those who do use it would behave differently in the face of its abolition. "Hardened criminals will always have their excuses and alibis ready, but innocent and confused people will be at greater risk of being wrongly convicted and imprisoned," Liberty argues.
Liberty believes that taking away the rights of suspects will have no impact at all on the causes of crime, and in any event the right to remain silent is exercised by only a very small minority. (A Royal Commission study of 1983 showed that only 4.5 per cent of those interviewed used to the right and half of those were convicted.)
In research published last May, the all-party law reform group Justice reported evidence that the removal of the right to silence failed to assist in the fight against serious crime. Its research showed that crime clear- up and conviction rates in Northern Ireland had in fact declined since the removal of the right of silence five years earlier. Justice also said that trial judges were giving great weight to silence and in some cases treating it almost as a presumption of guilt.
The legality of the abolition of the right to remain silent has yet to be tested. Neither Ernest Saunders nor John Murray is exactly about the right of silence in the 1994 Act, but, says John Wadham of Liberty: "Both decisions could force the Government to repeal the 1994 legislation."