Sent by Dave this picture shows a successful Model 18 racer, judged by the size of the trophy on the tank!
The photo was taken in Sydney at the speedway track; cinders were used on the track in these days, hence the bike and rider are still relatively clean.The rear brake drum has been removed; this was common practice at Brooklands to save weight but even then a dummy belt rim brake would be fitted to provide at least some means of braking in emergencies; apparently there is very little need for braking in speedway.
Updated: a correct description can be found following this link.