OS Net is our highly accurate and resilient network of global navigation satellite system (GNSS) base stations covering Great Britain. It enables Real-time Kinematic (RTK) positioning services, offered by our partners, which are ideal for surveying, construction and precision agricultural applications. OS Net raw data is available free of charge for post-processed positioning. The datasets consist of station locations and actual data, which is currently archived at Nottingham University.
https://www.ordnancesurvey.co.uk/business-government/tools-support/os-net-tools