IN ITS fight against crime, the Serious Fraud Office has enjoyed a much-feared power not granted to the police — the compulsory interview. This allows its investigators to require someone to attend an interview and answer questions believed relevant to an investigation. But a recent ruling in the first trial of the former directors of the Wickes DIY chain has dealt a blow to the use of this potent weapon in the fraud-fighters’ armoury.

The power is contained in Section 2 of the Criminal Justice Act 1987 and Parliament has increased the number of agencies that can exercise it — reflecting its importance to investigators. Last month it was granted to the Office of Fair Trading in the context of investigating a criminal cartel. The Act tries to restrict almost to vanishing point the lawful excuses for refusing to co-operate. Penalties for refusal are severe.

However, the power raises the key issue of self-incrimination. In the case, brought by the former Guinness chief Ernest Saunders, before the European Court of Human Rights, the court ruled that any answers given under compulsory questioning cannot normally be used at the defendant’s trial. So it would be unlawful for a prosecutor to seek to adduce a transcript of any interview in evidence.

In Wickes, though, it was the co-accused who wanted to introduce a transcript, as evidence of the guilt of another co-accused. The judge held that the co-accused’s right to use the interview as evidence of his own innocence could not be abridged. Faced with such a collision of defendants’ rights, the only solution, the judge ruled, was separate trials.

The ruling has wide implications. A compelled interviewee could now have a right to refuse to answer questions, if he has a well-founded fear that the answers may be used later by a co-accused. Such a fear could be an excuse for silence — especially if the prosecutor refuses to agree to separate trials. The Wickes case has exposed an important lacuna in the law. But it could become a headache for fraud prosecutors.

• The author is a solicitor at Corker Binning

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