This is not the accustomed place for a discussion on constitutional practice and usage in the United Kingdom, but a short primer may not be out of order.
FighterBoy wrote:Why did Thatcher decide who's British and not the Queen?
Thatcher didn't either. The acquisition of British nationality is governed by rules issued under the British Nationality Act 1981 that were passed by Parliament, not by Mrs. Thatcher.
The grant of British nationality has always been a gift of Parliament, not of the Queen. The Queen-in-Council (essentially the C abinet) could in earlier times grant the status of denizen, which would give the person settled status in the UK. So, in modern times, it would be the equivalent of ILR/PR. But full citizenship has always required an Act of Parliament.
FighterBoy wrote:passports (but not nationality) are the prerogative of the Queen.
Passports are not the prerogative of the Queen, they are issued under the Royal Prerogative. The Royal Prerogative is a source of law and is not associated with the Queen any more than the Royal Courts of Justice.
The Royal Prerogative is exercised by the Queen's ministers in her name, just as judges dispense justice in the name of the Queen, but without her actual involvement. Under current constitutional usage, the ministers are accountable to Parliament (generally the Commons, but also the Lords) and can be questioned on their exercise of the Royal Prerogative. As a source of law lower than statute, it can be overturned by an Act of Parliament and can also be examined by the courts.
FighterBoy wrote:nationality law was made into a function of immigration law
Nationality law and immigration law are separate and distinct. It is unfortunate that most people using these forums see them as one continuum, whereas in reality they are separate and distinct.
Non-EEA immigration (from visit visas to ILR) is governed by the Immigration Act 1971 while EEA nationals and their dependents by the European Communities Act 1972. The various types of British nationality are governed by the British Nationality Act 1981. It is amended, from time to time, by other Acts of Parliament.
FighterBoy wrote:Or, why not decide by public referendum?
Because in the UK constituition, it is the Queen-in-Parliament (that is, the Queen, the Lords and the Commons acting together) that is sovereign. The enacting formula for Acts of (the UK) Parliament makes that very clear;
"BE IT ENACTED by the Queen's [King's] most Excellent Majesty, by and with the advice and consent of the Lords Spiritual and Temporal, and Commons, in this present Parliament assembled, and by the authority of the same, as follows:—"
Legislative rules mean that there can be a thorough debate, including a line-by-line debate, of Bills. While the government can ram Bills through the Commons, because of its built-in majority, the Lords do a more thorough job of the line-by-line scrutiny and often many improvements to Bills, such as allowing the children born to British mothers before 1983 to register as British citizens, come from the unelected Lords.
Pure democracy is no panacea. Switzerland is a case in point. To gain Swiss citizenship, one needs federal, cantonal and local community approval. And while the first two are relatively straightforward, many local communities (boroughs/cities) give their approval by having a referendum on each individual applications. So, it is possible that two people meeting identical requirements may have different results for their naturalisation applications because the public approved one and rejected the other. And as there is no standard to meet but public approval, it is a bit like shooting in the dark. And even the courts won't override public will.
I remember reading on another forum about a migrant woman, the mother of Swiss citizens, being rejected for 12 years continuously.
FighterBoy wrote:
Also it meant by law, a prince couldn't pass on his nationality with a non Brit mother out of wedlock.
Rules for both the nationality and marriages of members of the Royal Family is governed by different laws, such as the Royal Marriages Act 1772, which was only repealed and replaced in the last Parliament.
As an aside, it is Parliament who decides who the King or Queen will be. So, if in theory, Prince Charles does not wish to be King and wants William to take over, the Parliaments of all 17 Commonwealth Realms (the countries that have the Queen as their head of state, such as Canada, Australia, New Zealand, Jamaica, Grenada, etc) must agree before he (Prince Charles) can step aside. So, you can see that even choosing who will be King or Queen is not within the Royal Prerogative, but is in the gift of Parliament.
I am not a lawyer or immigration advisor. My statements/comments do not constitute legal advice. E&OE. Please do not PM me for advice.