Following concern about the availability of plans, castings and tracks on which locomotives could be run, Paul Wiese arranged for a meeting in May 1975 to which all interested parties were invited. The result was the founding of the Association, the stated aims of which were to promote interest in the gauge. The Association now looks forward to the future knowing that the interests in this historic scale are safe.

From early times, locomotive plans and constructional article reprints were made available to members. Also, a number of patterns are donated or especially made to enable new locomotives to be built. Following the purchase of the 2½" gauge related patterns and residual stock when Dave Goodwin retired, the Association gives members an excellent range of iron and gunmetal castings. Acquisition of the Alan Headech wheel castings in 2009 means the Association now has a very extensive range.

Locomotive rallies hosted by an ever growing number of clubs who have 2½" gauge running facilities are held in various locations throughout the country between May and October when members can bring their locos and steam them or just put on display. The South East Area holds a meeting (get-together) in October for members to have an informal chat and display their latest efforts. Guest speakers are often booked. In 2007 a very successful GTG was held in Birmingham, and others followed.

The Association usually attends a number of exhibitions each year - the Guildford MES Steam Show in July, followed by Bristol in August. Then the Midlands ME in October and the Model Engineer Exhibition at Sandown in December.

A bimonthly newsletter (printed in colour during 2009) is sent to all members acquainting them of future events, the latest news and reports of rallies or meetings. In addition, the Journal is produced three times a year with an interesting mix of articles on matters relating to the 2½" gauge.

In recent years, several new locomotive designs (Saint Brides Hall and Toby) for members to build have been serialised. Also, Peter Gardner was persuaded to describe the design and building of his remarkable Stirling 8ft Single. During 2005-6, the Association promoted the revival of LBSC's Ayesha design, subsequently serialised in THE MODEL ENGINEER magazine. Drawings and patterns have been made to enable the builder to create either Ayesha (as LBSC built her or as described by LBSC in English Mechanics) or as a scale model of the Southern (Marsh designed) H2 or as the GNR Ivatt design. In 2007, the Horwich Crab 2-6-0 was serialised. In 2008, an electric powered BR Class 66 diesel outline was begun with sets of water-jet parts made available. 2009 saw the introduction of Peter Wardle's Baddesley Colliery Garratt.

Work on the Southern rMN class pacific is planned for 2010.