Details of MI5 surveillance techniques, not previously acknowledged, were revealed last week in a Northern Ireland court case involving three men accused of serious charges, including conspiracy to murder police and prison officers. When the judge asked for more details about a vehicle tracking device that had been used to gather evidence, the Public Prosecution Service refused to reveal the information to the defendants despite the judge's order, and the case collapsed.

The MI5 operation, which lasted three years, required 45 MI5 officers (apparently known as "Pins"), 35 Northern Ireland police officers (known as "Oscars"), and cost millions of pounds in total. It involved the use of audio surveillance and tracking devices fitted to vehicles, a helicopter, and possibly drones, too, according to a report in The Irish News. "Information from bugs planted in the cars was 'overlaid' with GPS co-ordinates from trackers, meaning surveillance teams could identify the exact time and location comments were made. Video footage, at times reconstructed by the [Police Service of Northern Ireland], was also added to the computerised exhibits to recreate what could be seen from the vehicles at the location and times conversations were held."

In the past, a similar reluctance to reveal how key evidence was obtained has led to the UK government being forced to drop cases and pay compensation. A desire to avoid this problem was one of the main motivations for introducing secret courts in 2013—ironically, just a week after the first Snowden revelations about massive surveillance by both GCHQ and NSA. Given that we already know so much about how intelligence agencies spy on people, it seems absurd that the UK government is still prepared to waste hard work by 80 of its agents, costing millions of pounds, in an attempt to pretend that MI5's techniques are still completely top secret.

It would be far better to return to traditional open courts, where defendants are allowed to see all the evidence against them, including information about how it was gathered. That would not only bring back traditional justice, in which people have a right to know and challenge evidence being used against them, but would also probably lead to those accused of serious crimes being convicted, rather than being paid massive compensation when cases collapse.