Fury and outrage – but not surprise – were the emotions expressed by most criminal lawyers this week to the disclosure in The Times that a solicitor’s conversation with his client, a prisoner serving life, had been bugged by the police.

The reaction of Jim Nichol, of Taylor Nichol, the London law firm, was typical. “It is outrageous. But since this practice was disclosed in a crown court trial a few years ago, I have always taken precautions – lowered my voice and spoken in a whisper – when communicating with clients in prisons or police cells.”

That case was in 2004 and involved a prosecution of 11 alleged drug dealers. The prosecution was dropped after it emerged in court that the police had bugged a defendant’s conversation with his solicitor, in breach of the principle that communications between a lawyer and client are privileged.

Judge Michael Heath, sitting at Lincoln Crown Court at that time, condemned the actions revealed as a “fundamental breach of human rights”. He went on to say: “Deliberate police bugging of privileged conversations between solicitors and an accused is outrageous.”

Despite the judge’s strong words and the loss of the case, defence solicitors and barristers alike said this week that they would not feel confident that such bugging did not still take place. As John Cooper, a criminal barrister on the Bar Council put it: “if I was dealing with a terrorist or other sensitive case, I would assume that my client was being bugged – as a matter of good precautionary professional practice.”

And if any evidence from such bugging emerged in court, then – lawyers agreed – it should be thrown out, as in the Lincoln case. “That,” said Nichol, “would serve the police right.”

What, though, of evidence legally obtained through bugging – of intercept evidence, for instance?

This week’s row over surveillance kicked off with the alleged bugging by Scotland Yard of conversations between the Labour MP Sadiq Khan and a constituent accused of terrorist offences – and then escalated to the disclosure about the solicitor (Simon Creighton) and his client (lifer Harry Roberts). But it was quickly eclipsed by news about bugging or surveillance of a different kind.

The long-awaited report by a committee of Privy Counsellors led by the former permanent secretary, Sir John Chilcott, concluded that evidence of crimes obtained through intercepts should in principle be admissible in court. “We believe,” they said, “a legal regime could be devised that should be ECHR [European Convention on Human Rights] compatible.”

The report was widely welcomed by groups such as Liberty and Justice, which have long campaigned for the use of internet evidence in trials. Eric Metcalfe, policy director of Justice, said: “It’s not rocket science: the intelligence services in the United States, Canada and Australia have coped with intercept evidence for many years. A suitable legal model should not be hard to find.” Shami Chakrabarti, director of Liberty, said: “If they can use phone taps all over the world without compromising security, why shouldn’t we?”

But the report was heavily couched with caveats. Firstly, security services and police will have a veto on whether a prosecution using their intercept material shall proceed. Secondly, any material is only to be disclosed (beyond judges, prosecutors, special defence advocates) in a form agreed by the security services. Finally, a “significant proportion” of internet evidence would not be available because of the need to protect techniques and capabilities, the report said.

A working party is to be set up to see how a scheme could operate in practice. One model proposed would use a version of the existing public interest immunity system (PII) to protect sensitive material being disclosed to the defence.

Police and security services are still opposed to the idea; arguing that techniques will be compromised and that the usefulness of intercepts in crime detection far outweighs any benefit as evidence in court.

The report itself accepts that benefit might be minimal: a review of cases in 2006/07 involving interception found that a change in the law would have boosted the conviction rate by just 4 per cent, from 88 per cent to 92 per cent. Use of intercept would result in 25 to 30 extra convictions a year across the UK: “mainly of second and third tier organised criminals (ie, not the most important targets.” The top targets of terrorist or criminals generally avoid the risk of intercepts, it said. And, finally, intercept use would not have helped a prosecution to be brought with any of the current “control order” suspects.

Yet the Crown Prosecution Service, led by Sir Ken Macdonald, QC, argued that such evidence can affect the course of a trial. Criminals are more likely to plead guilty early, realising their case is hopeless when their own words are played back to them. Despite the different legal context, the success in other jurisdictions – such as the US authorities’ convictions of the heads of all five New York mafia families – cannot be ignored, the report says.

Perhaps the biggest impact, though, is in the wider context of the fight against crime and terrorism. Gordon Brown takes the view that relaxing the ban on intercept evidence is just one tool in the armoury; and that it is still necessary to extend the time that suspects can be held pre-trial without charge. But opponents may argue that their case is now bolstered: that the need for exceptional measures such as control orders and extended pre-trial detention diminish if more of the guilty can be brought to trial. Allowing intercept evidence may kill off fresh moves to extend detention before trial.

However, the greater the use made of surveillance material, the greater confidence the public must have in the way that it is obtained – and the greater the need to know who, whether suspects or solicitors, is falling within the scope of those who gather it.

The UK is almost alone in having no judicial authorisation of surveillance activity. If this evidence is now to be used in court, then it is time, say groups such as Liberty and Justice, to remove the police and politicians from this task and hand it to the judges.

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