  Measurements of neutron beta decay observables required to determine
$|V_{ud}|$ are reaching the 0.1% accuracy. In this paper we review the
calculation of the decay rate of this process, discuss its relevant
uncertainties, and obtain an expression that is precise at the $10^{-4}$ level.
Our analysis clearly shows the necessity of measurements of $\lambda$, the
ratio of axial/vector couplings. The current situation in neutron beta decay is
that one cannot yet quote a single consistent value for $|V_{ud}|$ from it. We
also discuss the region of parameter space in the $|V_{ud}|$--$\lambda$ plane
where new physics effects should lie, if they contribute to neutron beta decay.
