  We describe the Sr optical lattice clock apparatus at NPL with particular
emphasis on techniques used to increase reliability and minimise the human
requirement in its operation. Central to this is a clock-referenced transfer
cavity scheme for the stabilisation of cooling and trapping lasers. We
highlight several measures to increase the reliability of the clock with a view
towards the realisation of an optical time-scale. The clock contributed 502
hours of data over a 25 day period (84% uptime) in a recent measurement
campaign with several uninterrupted periods of more than 48 hours. An
instability of $2\times10^{-17}$ was reached after $10^5$ s of averaging in an
interleaved self-comparison of the clock.
