Those holding the power – the prime ministers who lead the government when their party achieves a parliamentary majority – come and go with the vagaries of election, while the Queen endures as head of state. She lacks the power to govern, but she has a sort of negative power. Because she is there, no prime minister can be number one.
“She makes a dictatorship more difficult, she makes military coups more difficult, rule by decree more difficult,” said Robert Gascoyne-Cecil, the 7th Marquess of Salisbury, a Conservative politician and former leader of the House of Lords. “It is more difficult because she occupies space, and due process must be followed.”
– Sally Bedell Smith, Elisabeth the Queen. The Life of a Modern Monarch, 2012.