In previous posts I told the story of how Britain’s curfew tagging system can fail. Some prisoners are released early provided they wear a tag to enforce a curfew, which typically means that they have to stay home from 7pm to 7am; some petty offenders get a curfew instead of a prison sentence; and some people accused of serious crimes are tagged while on bail. In dozens of cases, curfewees had been accused of tampering with their tags, but had denied doing so. In a series of these cases, colleagues and I were engaged as experts, but when we demanded tags for testing, the prosecution was withdrawn and the case collapsed. In the most famous case, three men accused of terrorist offences were released; although one has since absconded, the other two are now free in the UK.

This year, a case finally came to trial. Our client, to whom we must refer simply as “Special Z”, was accused of tag tampering, which he denied vigorously. I was instructed as an expert along with my colleague Dr James Dean of Materials Science. Here is my expert report, together with James’s report and addendum, as well as a video of a tag being removed using much less than the amount of force required by the system specification.

The judge was not ready to set a precedent that could have thrown the UK tagging system into chaos. However, I understand our client has now been released on other grounds. Although the court did order us to hand back all the tags, and fragments of broken tags, so as to protect G4S’s intellectual property, it did not make a secrecy order on our expert reports. We publish them here in the hope that they might provide useful guidance to defendants in similar cases in the future, and to policymakers when tagging contracts come up for renewal, whether in the UK or overseas.