So, returning to my hypothetical example which got hijacked yesterday.
There is very little inherent legal protection for our rights in this country. If we opt out of the ECHR etc. then Parliament can do whatever it wants. There is no overarching domestic protection.
So, to take an extreme example to highlight the principle. If a government wanted to bring in a law making torture legal, there is nothing to stop them. First they would need to pass the law through the House of Commons. If they didn't have enough votes in the House of Lords, they could use the Parliament Act. That would mean the government would have to wait for 12 months before the law became legal.
Once it was passed, there would be no way for the law to be challenged in the courts.