To be clear - German nationals can be extradited to other EU countries under German law, but not third countries like the UK.
If the UK had remained in the EU, then extradition might be possible (depending on whether courts approve it) but right now it's pretty unambiguously impossible.
IANAL but there appears to be an agreement between the UK and Germany. Not sure if it’s just criminal cooperation, or whether extradition is part of that:
Not a lawyer, but that seems to be from the 60s and a quick Google search showed some court decisions that extraditions to the UK are not possible as staying silent can harm your defense, which contradicts German basic law where it states: "No German may be extradited to a foreign country. The law may provide otherwise for extraditions to a member state of the European Union or to an international court, provided that the rule of law is observed."
I’m sure they won’t, but it might be annoying to never be able to take a flight that connects in London for the rest of your life.
I have no idea if this is a likely or even possible consequence, but that’s one way lots of people have gotten ensnared by the long arm of the law, even when jurisdiction is otherwise normally lacking.
Not at all. Many people avoid Heathrow because it's a terrible airport and many more because they don't want to submit themselves to the UK justice system, which is as classist and corrupt as they come.
You also have no human rights in British Airports. The state can just randomly decide to question you. They'll force you to hand over passwords to all electronic devices and slap you with a terror offence if you don't comply. You won't even have the right to remain silent.
You'd be well advised to avoid a country this like.
