4mm = 1foot, 16.5mm guage.
The "OO" layout features double track running with a large storage yard. A single track branch to a small station and goods yard is also featured.
The layout can be operated DC or DCC and acts as a test track for members locos.
Although a British Outline layout, it's not unusual to see an American or Continental prototype being test run (providing it can fit through the tunnels).
The layout has been exhibited at a number of local shows over the last few years.