the United Kingdom is a Democratic system that uses a different form of government to organize itself.
In the United Kingdom, the people elect members of parliament.
From the rolls of Parliament, the Prime Minister is chosen.
The Prime Minister is the Chief Executive of the United Kingdom and can be removed if their coalition fails.
This is compared to the US where we elect both of representative and our Chief Executive who does not have to have a relationship with our legislature, which is a separate branch.
As a result, one could argue that less gets done as the Executive has no experience negotiating from within the ranks of the legislative branch.