The answer it seems is that the philosophy is that expounded by Finnis in an echo of de Maistre. He claims that -
The philosophy of law is not separate from but dependent upon ethics and political philosophy, which it extends by that attention to the past (of sources, constitutions, contracts, acquired rights, etc.) which is characteristic of juridical thought for reasons articulated by the philosophy of law. Positivism is legitimate only as a thesis of, or topic within, natural law theory, which adequately incorporates it but remains transparently engaged with the ethical and political issues and challenges both perennial and peculiar to this age. The paper concludes by proposing a task for legal philosophy, in light of the fact that legal systems are not simply sets of norms.If, like me, you are underwhelmed by the way that Finnis confuses personal idiosyncracies for timeless truths you might want somewhat more substance than a whinge about the supposed "oppression of critics of homosexual conduct" or scarewords such as communism.
Though, as has been said above, law and legal philosophy has a quasi-distinct domain and technical character, the very idea (concept) of law (an idea without which no laws will be made or maintained) is so dependent upon wider principles of moral and political thought and philosophy that neither law nor its philosophy can avoid engagement with the ethical and political issues and challenges of the age. Particular aspects of our law‘s content (including its procedural rules and institutions) can ameliorate, or in other cases harm and exacerbate, our community‘s common good. The legal instrumentarium can, not infrequently, provide an easy route to destructive social changes, as the apparatus of human rights litigation has, in many places, provided an easy route to abortion, euthanasia, damaging immigration, and same-sex marriage, to the oppression of critics of homosexual conduct, and to other destructive evils. But what social elites desire can very often be achieved without much resort to that instrumentarium, or even in defiance of it.
It seems to me that the task of legal philosophy today is twofold. It must keep clear its intrinsic relationship with, and dependence upon, all the truths of moral and political philosophy, not least by providing a constant critique of every form of legal philosophy that denies or distorts that relationship. And by its mastery, and its foundational explanatory understanding, of the law‘s technical instrumentarium it must remain in a position to criticize and expose – in the hope of deflecting -- every manipulation of it for purposes destructive of the common good, a good that includes but is not exhausted by the upholding of juridically cognizable rights.
Of special importance in the coming decades will be a recovery of awareness amongst legal philosophers that law‘s paradigmatic form, the ius civile, is the law of a people, posited by a constituent act (or constitutive custom) and ongoing legislative acts of their self-determination as a people, acts which can and should be consistent with their obligations to do and respect right (human rights, as contained in the ius naturale) and their responsibilities towards other peoples and those other peoples‘ self-determination, rights and needs. Just as countless thinkers in the nineteenth and twentieth centuries too casually assumed the justice of communist notions of a propertyless community, notions inadequately attentive to the long-term conditions of a sustainable, prosperous and just society of free persons, with the result that countless millions of people suffered more or less directly from the application in their polities of these errors of practical thought, so likewise many thinkers today too casually assume (explicitly or implicitly) the justice of quasi-communist notions of a borderless humanity, notions incompatible with the long-term conditions of a sustainably just and civilly free political order and Rule of Law. Even in the short term, this kind of error of practical thought results in the kind of political community increasingly familiar, whose peoples‘ multi-cultural internal diversity of ultimate allegiances is both promoted and countered by an ever-growing apparatus of security and surveillance, a severe diminution in freedom of political and intellectual discourse, and an explosion of law-making and regulatory bureaucracy indifferent to the benefit of having a society whose self-determination takes in large measure the form of that sharing of expectations which Ulpian and Aquinas called common custom.
Practitioners of the philosophy of law may be especially susceptible to this kind of error, to the extent that they envision legal systems simply as sets of norms, rather than as the principles, norms and institutions adopted by a people extended in time and in territorial bounds, in more or less adequate fulfilment of its moral responsibility to do so.