The Guardian has been covering the issue of a supreme court for the UK. This is part of package of judicial reform proposals advanced by Lord Falconer of Thoroton, previously Tony Blair's flatmate and minister for the Millennium Dome and ID cards.
The proposals concern, inter alia, the status of the Law Lords, and judicial appointments. Keeping judicial appointment apolitical and focused on judicial integrity is of critical importance, lest our judiciary go the way of America's. I am unsure whether the government's proposals are good or bad in this regard - their aims seem to include making the judiciary more "representative" of particular groups within UK society. Criminals constitute an important group within society, but are not so to be "represented" within the ranks of the judiciary, which strikes me at least as anomalous, but I can see how it might be justified.
The other "biggie" is the formal separation of judiciary and legislature, motivated by the "separation of powers" doctrine. I've never been a fan of the separation of powers idea, which was based on an 18th century author's misunderstanding of a foreign country's constitution. That foreign country was in fact England (the author was French), but of course England, now part of the UK, has changed: the country is formally democratic and the role of legislation and regulation is now extremely different in its impact on people's lives. There is little real distinction between legislation and administrative practice, to the extent that having a government minister sitting as a judge might almost be justifiable. Nevertheless some, including, I believe, Lady Justice Hale, have claimed that the case for separation is "unanswerable".
There are three answers which suggest themselves to me: the doctrine of separation of powers is a bad idea in the first place, or, it is a good idea, but should be outweighed by other considerations, or, whether or not it is a good idea, this doctrine is unoffended by the current arrangements.
To take the last argument first, it should be observed that in practice, Law Lords do not operate as part of the legislature. Some abstain entirely from proceedings in the Lords in its legislative capacity, and the others constrain themselves to a marginal advisory rôle which they would occupy whether or not they were formally members ex officio of this effectively unelected body. It is a distortion to claim that there is anyone ruling on legislation he helped vote into being in the first place (all Law Lords are currently male, so "he" is appropriate). In real terms, there is no substantive conflict; the conflict is only a formal one.
The real offence against separation of powers in the UK consists in the relation between legislature and executive, not legislature and judiciary. The only check on executive power is the confidence vote in Parliament (and the threat to use it). Opposition to a particular feature of a particular policy can only be achieved at the expense of bringing down the whole Government. The demands of responsible continuity of government, combined with the particular form (inchoate) legislative control of the executive happens to take in the UK, necessitate executive control of the legislature through tight party discipline and the whip system. The UK executive lacks the fixity of tenure secured by systems such as the American, and thus must subordinate the legislature to maintain itself in power, nor does the constitutional settlement provide for any judicial check on what legislation may emanate from this arrangement. It is the political temperament of society, and constitutional checks and balances in the detail of political arrangements, not separation of powers in the overall structure, which serve to protect the legitimate interests of individuals, community and society. If there is a relation between the three branches of government to be reformed in line with the separation of powers doctrine, it is not that between legislature and judiciary.