The United Kingdom has the world's second-largest economy by purchasing power parity.
The United States is the world 's largest national economy in nominal terms and second largest according to purchasing power parity ( PPP ) , representing 22 % of nominal global GDP and 17 % of gross world product ( GWP ) . United Kingdom . The United Kingdom is a developed country and has the world 's fifth-largest economy by nominal GDP and ninth-largest economy by purchasing power parity .