Harrow and Wembley Model Engineers

Harrow and Wembley Society of Model Engineers have a permanent ground level multi-gauge track network, consisting of 31/2,  5 and 71/4 inch gauge and a continuous run. The the minimum curve radius, 54 ft (16.5 m).  The length is 1200 ft (366 m) continuous or 2270 ft (692 m) out and back to terminus.
http://www.hwsme.org.uk/