About government and parliament
A government with too much power.
A parliamentary system should put parliament at the centre, accountable only to the voters. In the UK parliament is weak in the face of government power, and that's largely because of the Crown and the monarchy.
The Crown gives the government huge powers to take decisions without parliament or to control parliamentary business, whether that's deciding when parliament will be running or having the power to ensure proposed laws they disagree with have little chance of getting passed.
The monarchy also denies us an independent, effective head of state. That means there is little check on the use of royal powers and no-one to arbitrate during political crises. It's like having a football match with no referee.
Parliament is weak in the face of government, largely there to do what it's told. But in terms of the power of make laws, change our constitution and determine our rights, parliament is all powerful.
In the UK parliament is sovereign, which means it's the highest power in the land. No court can overturn a decision made by parliament, no treaty can override laws passed by parliament. A court could rule that a law conflicts with a treaty, or with another law, but a judge can't override or scrap that law.
That's not how a democracy should work. Parliament is there to work for us, not to rule over us. And given the control government has over parliament, the current constitution ends up concentrating huge amounts of power in the hands of the Prime Minister and government ministers.
In terms of domestic law the British government is one of the most powerful in the democratic world.
A real parliamentary democracy
The answer to this is simple enough. There's no need to throw the whole constitution out the window. We just need to make every part of it more democratic and re-balance power between people, parliament and government.