It has most prominently been utilised, often alongside Article 8 of the Convention, to challenge the denial of same sex marriage in the domestic law of a Contracting state.
[16] Mowbray argues that the doctrine is the product of subsidiarity: "it is a technique developed to allocate decision-making authority to the proper body in the Convention scheme to delineate in concrete cases the boundary between "primary" national discretion and the "subsidiary" international supervision.
"[24] Hutchinson explains that in practice the margin of appreciation as to a State's domestic implementation of Convention standards can become wider or narrower depending on the surrounding circumstances of the alleged breach being heard by the Court.
[25] Derogations from the Convention ultimately rest on the concept of domestic necessity in Contracting State societies, and so a natural consequence becomes situation-oriented margins of appreciation.
In more than one case, the Court has said that in relation to Article 12, Contracting states enjoy a "particularly wide" margin of appreciation in determining the measures necessary for Convention rights such as this one to be secured within their jurisdiction.
[30] The government maintained that both the clear wording of Article 12 and the Court’s case-law as it stood indicated that the right to marry was by its very nature limited to different sex couples.
[31] The Austrian Government conceded that there has been significant social changes in the institution of marriage since the adoption of the Convention, but there was not yet any European consensus on granting same sex couples the right to marry.
[33] As matters stand, the question whether or not to allow same sex marriage is to be left to regulation by the national law of the Contracting State,[34] and no violation of Article 12 was found.
The right was granted in the context of strictly traditional concepts of marriage and a lack of European consensus upheld the wide margin of discretion afforded to Contracting states.
"[39] It ultimately fell within the Contracting States margin of appreciation as to how to regulate the effects of the change of gender on pre-existing marriages,[40] and consequently Article 12 had not been violated in either of these cases.
[50][51] The UK Government maintained that neither Article 12 of the Convention, nor the closely related Article 8, required a state to permit a transsexual or transgender person to marry a person of his or her original sex: "if any change in this important or sensitive area were to be made, it should come from the UK’s own courts acting within the margin of appreciation which this Court has always afforded.
"[52] The Court considered the terms of Article 12 which referred to the right of a "man and a woman" to marry no longer had to be understood as determining gender by purely biological criteria.