A person is not qualified to be appointed a judge of the Supreme Court unless he has (at any time)—
held high judicial office for a period of at least 2 years,
been a qualifying practitioner for a period of at least 15 years.
satisfied the judicial-appointment eligibility condition on a 15-year basis, or
been a qualifying practitioner for a period of at least 15 years.
A person is a qualifying practitioner for the purposes of this section at any time when—
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
he is an advocate in Scotland or a solicitor entitled to appear in the Court of Session and the High Court of Justiciary, or
he is a member of the Bar of Northern Ireland or a solicitor of the Court of Judicature of Northern Ireland.