  (Abridged) Star-forming nuclear rings in barred galaxies are common in nearby
spirals, and their detailed study can lead to important insights into the
evolution of galaxies, their bars, and their central regions. We present
integral field spectroscopic observations obtained with SAURON of the bar and
circumnuclear region of the barred spiral galaxy M100, complemented by new {\it
Spitzer Space Telescope} imaging of the region. We use these data to enhance
our understanding of the formation, evolution, and current properties of the
bar and ring. We derive the kinematics of the gas and the stars and quantify
circular and non-circular motions using kinemetry. We analyse this in
conjunction with the optical and infrared morphology, and our previously
published dynamical modelling. By comparing line indices to simple stellar
population models we estimate the ages and metallicities of the stellar
populations present within the region, especially in and around the ring. Our
kinematic and morphological results all confirm the picture in which the
nuclear ring in M100, considered typical, is fed by gas flowing in from the
disc under the action of the bar, is slowed down near a pair of resonances, and
forms significant amounts of massive stars. Detailed stellar population
modelling shows how the underlying bulge and disc were put in place a number of
Gyr ago, and that the nuclear ring has been forming stars since about 500~Myr
ago in a stable succession of bursts. This confirms that nuclear rings of this
kind can form under the influence of a resonant structure set up by a bar, and
proves that they are stable features of a galaxy rather than one-off starburst
events.
