Jampot refers to the slang term given to the rear suspension of 1950's motorcycles, and is the name of the club's journal. The name has been adopted by a good many affiliated clubs throughout the world, many of which are listed on the club's site and also at Bikelinks under Classic Clubs.
From their website:
The AJS & Matchless Owners Club Limited caters for individuals and families who have an interest in either AJS or Matchless motorcycles. The club produces its own monthly magazine (called Jampot) that is distributed to over 3,600 members worldwide as well as having its own spares scheme to assist owners in keeping their machines in top working order.
A number of social activities are organised at international, national and local levels. Each year members of the club organise an International Rally in May, a UK National rally in August and a second national 'back-to-basics' rally in October. as well as these rallies, there are a number of local sections throughout the UK that organise their own social evening and week-end activities.
There are also numerous archives including one on the famed AJS OHC V-twin (pdf)