Great Britain Philatelic Society - www.gbps.org.uk
The Royal Philatelic Society London - www.rpsl.org.uk
The British Postal Museum & Archive - postalheritage.org.uk
The British Library - www.bl.uk/reshelp/findhelprestype/philatelic/philateliccollections/philatelycollectionshub.html
MJ Publications - www.mjpublications.com