OS Open Rivers from Ordnance Survey is a mid-scale topologically connected watercourse network dataset covering the UK. OS Open Rivers includes inland and tidal rivers, canals and connecting source, junction and outlet nodes.
OS Open Rivers can be combined with other OS datasets, such as OS Open Map Local or OS Vector Map District to provide map reference data. It can also be used for spatial analysis and basic network analysis, such as tracing.
GIS4BUSINESS is an OS Partner and can supply OS Open Rivers data in most major formats and for the coverage you require, from a small area to full UK coverage.