osmgb.org.uk) was an organisation which aimed to serve certain OpenStreetMap needs in the Great Britain. It was not attempting to be a GB Chapter (See UK Group)
Set up by Steven Feldman in mid 2011  prompted by late night conversations at SotM 2010 in Girona, and working with folks from Nottingham university GIS group, OSMGB has focussed on setting up some "enterprise friendly" WMS WFS type services using OpenStreetMap data with the intention of bridging gaps to help engage particularly with UK local councils. The project aimed to explore the potential for applying rules based quality improvement to OSM data and identifying whether a more formal quality assurance model encourages usage and ultimately contribution from the public sector.
There used to be a OSMGB wiki at osmgb.org.uk/osm-gb-wiki which had details on web services, infrastructure and project governance. And there used to be a blog at http://lgosmgb2.nottingham.ac.uk/blog/ with contributions from Amir Pourabdollah, the lead researcher, and members of the steering group.
The OSMGB organisation bagged a name which might have been chosen for a Great Britain chapter organisation. Now that this organisation is being wound down, the name is kind of coming available again. See GB/UK group naming question for more on naming of that organisation.