Neither the United Kingdom nor the United States are true democracies. However, the United States wins over the United Kingdom because it is is a true representative constitutional republic. The United States doesn't have laws shielding its lawmakers or lawmaking chambers from press scrutiny like the United Kingdom does. That's just one example.
I believe the United Kingdom is coming very close to functioning like a true democracy but they still have the remains of a monarchy. Overall I would say the United States is closer to the true ideals of a democracy. However, I think examining our system in the current political climate shows many of the draw backs to democracy rather than it's strong points.
Neither the United States or the United Kingdom are a true democracy. In a true democracy, there are no representatives of the people, everything is simply decided by popular vote. If laws are decided by representatives who are voted in, then the government is actually a Republic, not a democracy.
Because the UK uses a "majority rules" approach to its national elections, it is closer to being a true democracy than the US. The US is a republic that uses an electoral system to name its new president every four years, which means that it is possible to win the popular vote but lose the election as president.
The U.K. is the true democracy, between the United States and the United Kingdom, because in the United States, once a person is elected to office federally, they are like a king and they never lose their seat, being treated like royalty. In the United Kingdom, power changes hands when people want it to.