The only real constraints on Parliament's freedom of legislation are the body of EU law, and the European Convention on Human Rights. The former is variously directly and indirectly applicable in UK law, and the latter is enforced both by UK statute (which can be overridden by Parliament) and by oversight from an external court (which has limited enforcement powers).
I agree that the surveillance law is obviously bad policy, but it wasn't obviously in breach of either EU law or the ECHR. The English court of appeal thought that it wasn't, but referred it to the Court of Justice of the European Union for a binding opinion, because they decided the question was finely balanced. CJEU ruled that it was in breach of articles 7 and 8 of the Charter of Fundamental Rights of the European Union, so the Court of Appeal made a domestic declaration that the statute was in breach of EU law.
The full judgment is at http://www.bailii.org/ew/cases/EWCA/Civ/2018/70.html, if you're interested.
And if somehow a political leader has managed to corrupt/threaten 3 court levels, then you've got bigger things to worry about, and chances are such a person would take other measures to get rid of his political opponents that are much faster.
Also, it's not like you can't ever arrest a politician. There are laws and countries that do put politicians in prison, especially in cases on corruption.
In failed rule of law states, it has often happened that former politicians were/are criminalized. This can make losing power, in practice, directly lead to losing life & freedom. This then becomes a mandate to maintain power by whatever means necessary.
It also opens the door to political purges of oponenets.
I'll take an example from the Middle East (my home). When Saddam lost power, he was hanged. Gadaffi was lynched. Mubarak was imprisoned, then released when his faction came back into power. This creative an imperative for Assad to maintain power in Syria. Losing power is a death warrant for him, and he is willing to kill even more brutally to preserve himself.
In Israel, Netanyahu is under criminal investigation. He has immunity from prosecution while in power, but not from investigation. This is very dangerous and many analysts (including US generals and spooks) are worried he will start a war in order to consolidate power. tricky stuff.
These are not rule of law states, and they do not have independant judiciaries. But the principle stand. This is why I found (for example) Trump's threats to Clinton so disturbing. If he had followed up, the entire american system would be in danger.
Realistically, the process in place is there for a reason. Small crimes (eg Clinton's emails or Trump's contact with Russia, if it doesn't turn out to be worse than reported thus far) are swept under a rug. Large crimes (Clinton's BJ?) should be investigated through some non-criminal (courts are OK, the US system is suboptimal here) system where life and freedom are not at stake, just power.
Courts cannot be subsidiaries of executive-legislative power (even in the states where it is explicitely forbidden executive & legislative are not really seperate) but the opposite also cannot be.
It is ugly the way it is. We should be doing better. But, there really are fundamental issues here with the stability of democracies at stake.
If they were "criminalized" and no one had the power to lock them up, there was no rule of law in the first place. There was a dictatorship masquerading as a democracy.
"The Democratic People's Republic of Korea"
Politicians should not be above the law.
On the contrary, the public figures are supposed to be more transparent and held accountable more readily than private citizens.
The reason I argue the opposite (OP) is for practical rather than moral reasons. Morals are a luxury. Systemic stability is at stake and is a requisite for any rule of law.
That said, prosecuting legislators and/or political executives for ilegal legislation is far too dangerous, essentially merging all branches of government.
Parliamentary immunity also exists in many countries to ensure that parliamentarians cannot be prosecuted for acts they undertook whilst in office (or other acts, so they that they cannot be compelled into anything).
You’re never going to get a body politic to pass a law that places them all at risk, and if somehow one got through, they’d pretty quickly pass another one to repeal it.
Presumably she doesn't because she rather likes the money and the palaces more than she wants to settle the question as to how you have a parliamentary democracy and monarchy with "you don't".
Besides, the scenario you depict further reinforces my argument that there’s a “trusted root” at the apex of our democracies and that this entity (whether the Queen, or Parliament, or Congress, or the President, or whatever-have-you) can pursue its own interests with abandon, and there’s nothing we buggers further down the pyramid can do to prevent it.
It's far less terrifying to me that the present Queen can do that than that any oligarch with a £100M to spare can probably "lobby" to get the changes they want.
The royal family are in a dicey position, but I trust the current Queen more than MP s in general, but perhaps less than the 2 Houses as a whole. She can probably do anything that goes with either Parliament OR with the demos but couldn't go against both.
You're also misunderstanding the argument: It's not the powerful politicians that are frightening, it's the powerless. By prosecuting (former) politicians, you're not creating disincentives against abuse of power, you're disincentivising loss of power.
That's the hard-to-accept logic behind the mostly deferential treatment the Nixons and Mugabes of the world today get after they lost power.
>By prosecuting (former) politicians, you're not creating disincentives against abuse of power
Do you think prosecuting people who committed crimes creates a disincentive against crime?
>you're disincentivising loss of power.
The same could be said for (former) leaders of drug cartels and mafia bosses, but we still go after them (as well as the current ones), don't we?
Loss of power is already by default highly disincentivized, which is why people want to hold on to it for as long as they can. It's also why we enforce term limits and have checks and balances. However those checks and balances are quite toothless when you elevate politicians above the law.
"We hang the petty thieves and appoint the great ones to public office." -Aesop
Troops on the streets?
It's dangerous to criminalise political tier decisions and actions, just like it's dangerous to prosecute former politicians. It harms the ability to preserve peaceful transitions. Criminals or not.
First, it opens a door to political purging. Also incentives to use power in order to remain free is just too big.