This paper describes the features of the UK interbank system, using a newly available regulatory dataset on counterparty-level interbank exposures. To our knowledge, this dataset is the most granular representation of a large interbank market available worldwide. We present recently developed metrics which characterise the network from the point of view of financial-system stability. We pay particular attention to four complexities. Firstly, the network exhibits multiple layering: nodes are connected by up to 150 types of financial instruments, including prime lending, fixed income, CDS, repos, derivatives and others, at a spectrum of maturities. Secondly, each link is directed from bank A to bank B. Thirdly, each link has a weight, which corresponds to the pound sterling value of the exposure or funding source. Fourthly, nodes are diverse in their balance sheet characteristics. Comprehensive matching between the interbank exposures dataset, a regulatory balance-sheet dataset and public data allows us to capture this heterogeneity. The interbank network clearly exhibits a 'hub and spoke' structure. Most of the 176 banks resident in the UK are exposed to a handful of money-centre banks. We infer that the UK interbank system is 'robust yet fragile': it is resilient against random shocks, but vulnerable to targeted attacks. We conclude by suggesting avenues for future research, particularly on how financial policy might respond to such network structure in order to improve financial-system stability.