Parliament is supreme.
Note, this question is seeking more theoretical answers to the question than "realistic".
It is unwise to view the world through a theoretical lens, unless the intention is to improve the lens, rather than understand the world. But as you insist, let us look.
It seems that this is "carte blanche" for Parliament to override any other constitutional principle of the United Kingdom, at least for their own term
Your interpretation is, from a strictly legally theoretical basis, essentially correct.
Though, Parliament cannot change the weather.
First, there are some textbook exceptions, which we can get out the way early. For instance, if the UK Parliament repealed the Australia Act and decided to exert sovereignty over Australia again, that probably wouldn't hold water in the Australian courts. Parliament cannot change reality.
Parliamentary supremacy is regularly upheld by the judiciary.
Let us confine our question to those jurisdictions where the Crown-in-Parliament has practical authority. Can it make whatever law it wishes?
Yes, that is the idea of Parliamentary Sovereignty. The most recent affirmation of the long-established principle was given by the President of the Supreme Court in the leading judgment in R. (Miller) v. Brexit Secretary:
- This is because Parliamentary sovereignty is a fundamental principle of the UK constitution, as was conclusively established in the statutes referred to in para 41 above. It was famously summarised by Professor Dicey as meaning that Parliament has "the right to make or unmake any law whatsoever; and further, no person or body is recognised by the law as having a right to override or set aside the legislation of Parliament".
The judgment, which of course went against the Brexit Secretary, was rooted in the fact that Parliament is supreme. Parliament has, many times in the past, legislated in areas that the Article 50 notification would affect: therefore, the government could not take action which trod on Parliament's authority, even if there has been a referendum of the people with a clear outcome.
The Principle of Legality.
There is a check on Parliament's authority. It cannot make a generic law which gives away its power to someone else, unless it is totally clear about what power that person [or body] will have.
The Principle of Legality is most clearly summarized by Lord Hoffman in ex Parte Simms.
Parliamentary sovereignty means that Parliament can, if it chooses, legislate contrary to fundamental principles of human rights. [...] The constraints upon its exercise by Parliament are ultimately political, not legal. But the principle of legality means that Parliament must squarely confront what it is doing and accept the political cost. Fundamental rights cannot be overridden by general or ambiguous words. This is because there is too great a risk that the full implications of their unqualified meaning may have passed unnoticed in the democratic process. In the absence of express language or necessary implication to the contrary, the courts therefore presume that even the most general words were intended to be subject to the basic rights of the individual. In this way the courts of the United Kingdom, though acknowledging the sovereignty of Parliament, apply principles of constitutionality little different from those which exist in countries where the power of the legislature is expressly limited by a constitutional document.
Essentially "the principle of legality" says that if Parliament wishes to take away rights, it has to say so, in clear, explicit, and unambiguous language. Or the courts will ignore it.
It cannot be vague. If it is vague, the courts will assume that the lawmakers intended to safeguard existing rights and liberties and it will interpret the law accordingly.
For instance, in the case of HM Treasury v Ahmed, the Supreme Court had to decide if a law gave the King [now the Queen] power to freeze a terrorism suspect's assets. The wording was:
(1) If, under Article forty-one of the Charter of the United Nations [...] the Security Council of the United Nations call upon His Majesty’s Government in the United Kingdom to apply any measures to give effect to any decision of that Council, His Majesty may by Order in Council make such provision as appears to Him necessary or expedient for enabling those measures to be effectively applied, including (without prejudice to the generality of the preceding words) provision for the apprehension, trial and punishment of persons offending against the Order.
They decided, no it did not. The words to "make such provision as appears to Him necessary or expedient" were not wide enough to allow Him to make provisions for people only suspected of crimes.
Parliament subsequent passed a law explicitly undoing that judgment.
There was no answer to that---Parliament had spoken.
Parliament is not the government.
But Parliament is not the government. It is a body of many hundreds of people. It is split into two houses and several parties. One house considers itself the sensible, senior house with a duty to stop ill-thought-out ideas. The other spends most of its time preventing itself from conducting business. The executive may lead the legislature, but they cannot compel it. And indeed, the legislature may sack the executive, as Teresa May reminded us yesterday.