A ruling is due on a legal action over claims that the communications of two Green Party politicians are being intercepted by GCHQ.
The Investigatory Powers Tribunal, which considers complaints about the way public authorities use covert techniques, has heard a case brought by MP Caroline Lucas and Baroness Jones of Moulsecoomb, together with another former MP, George Galloway.
Lawyers allege their communications are being intercepted by GCHQ as part of the Tempora programme, which monitors and collates on a blanket basis the full range of electronic communications data produced in, or transiting through, the UK and other countries.
The communications it intercepts include emails and other internet traffic as well as telephone calls.
In July, counsel Ben Jaffey told the panel, headed by Mr Justice Burton, that the preliminary hearing, which was contested by the Security Services, was about what safeguards were required before members of the legislature were subject to intercept or surveillance.
It concerned the nature and scope of the Wilson doctrine and whether it, as currently applied, contained adequate safeguards to comply with Article 8 and Article 10 of the European Convention on Human Rights.
The Wilson doctrine, implemented by prime minister Harold Wilson in November 1966, provides that no MP's telephone shall be tapped unless there is a major national emergency, and that any changes to the policy will be reported by the prime minister to Parliament.
Mr Jaffey said: "The Wilson doctrine does not exclude any possibility of surveillance or intercept of MPs. Nor should it. MPs are human, as are judges, lawyers and journalists.
"But given their important constitutional function, strict safeguards to protect parliamentary communications are an important bulwark for the protection of the public interest."
He said that the current safeguards had not been properly implemented and were not adequate.