THE Wilson Doctrine was never as precise, far less as potent, as its title might suggest. Devised by Harold Wilson in November 1966 to reassure MPs that the security services were under control, it contained an important caveat from the beginning.

Simply put, the then Prime Minister reserved the right to allow the bugging of MPs’ telephones – a practice the doctrine was supposed to “ban” – if surveillance was warranted by the needs of national security. Mr Wilson promised only to inform MPs, at a time of his choosing, that he had granted an exception.

The position was not unreasonable. If no one suggests that parliamentarians should be above the law when “ordinary” crimes are suspected, no one can argue that national security is less important. If the data collected from communications is meanwhile truly incidental, modern objections can sound tendentious.

The “doctrine” was, in any case, no more than Mr Wilson’s personal order to the security services. As the Investigatory Powers Tribunal (IPT) has decided, it has no standing in law. The Green MP Caroline Lucas, and her colleague Baroness Jones, cannot therefore claim that their rights might be breached.

Case closed? Not quite. A parliamentarian stands in a special relationship to the state. If the job is to hold government to account, there must be protection against government power. That is the fundamental meaning of parliamentary privilege. Why a statement from the floor of the House should be protected while an MP’s email remains vulnerable is far from obvious.

There are, in any case, wider issues of privacy and confidentiality. In the case of parliamentarians, one touches upon the other. How would an MP assist an innocent constituent facing investigation under security laws if all communications provided “incidental” information to his accusers?

The IPT’s decision has been predictable since it became known in July that Wilsonian protection for MSPs, MEPs and other parliamentarians had been ended. We would now expect the security services to be monitored carefully in this matter.

We would add a further thought. If the Wilson Doctrine has been extinguished, perhaps the time has come to craft a replacement, acceptable to the security services and parliamentarians, to meet the needs of the modern world.