Royal Philatelic Society of London: http://www.rpsl.org.uk/
Bath Postal Museum: http://www.bathpostalmuseum.co.uk/
Colne Valley Postal Museum: http://www.cvphm.org/
The British Postal Museum & Archive: https://postalheritage.wordpress.com/tag/loughton/
British Library: http://www.bl.uk/collections/philatelic
Great Britain Philatelic Society: http://www.gbps.org.uk/
National Philatelic Society: http://www.ukphilately.org.uk/
British Thematic Association: http://www.brit-thematic-assoc.com/