He was arrested and charged with inciting the officer to distribute indecent photographs of children contrary to common law.

Lord Justice Tuckey, having reviewed the common law and academic opinion, considered that neither implied a requirement to prove shared intention as contended by Armstrong.

[5] Professor John Smith noted in commentary to the DPP v Armstrong case that the distinguishing of the troublesome ruling in R v Shaw [1994] – effectively shunning it – was to some logicians unconvincing but ingeniously pointed out the flaw in the indictment there which was a welcome way of largely overruling R v Shaw, a decision of court of higher official rank but similar bench of eminent judges, considered of binding, not persuasive precedent.

It has limited Shaw to its peculiar indictment's wording, which hinged on its poor construction in relation to an alleged theft incitement.

[5] The judgment noted and contrasted itself to the approved suggested state illegality scenario of framing a "young man" by a detection-target-seeking police officer and an agent provocateur, as envisaged by Lord Diplock in R v Sang in the highest court twenty years earlier.