I found this page on Udal Law, which is the old Norse law which still exists in some parts of Great Britain.

Highlights:

Udal Law still exists today, most apparent in the ownership of the coastline. Whereas in the rest of Britain ownership of land extends only to the High Water mark, in Orkney and Shetland this extends to the lowest Spring ebb, plus variously as far as a stone can be thrown, or a horse can be waded, or a salmon net can be thrown.


One interesting anomaly is the Mute Swan. About 1910 a Kirkwall lawyer was determined to prove that Udal Law still had force, and accompanied by his friend, the Procurator Fiscal, went out to Harray Loch and shot a swan. The case went to the High Court and the Crown lost. Everywhere else in UK the Crown owned the Swans - in Orkney they were, and still are, the property of the people as the Norwegian Crown never claimed such ownership. Nowadays we do not shoot swans, but the principles of the old Norse Udal Law still stand.

I wonder where else Feudal title supersedes modern law.

Thanks to Warren for bringing Udal Law to light.