At long last I have managed to find the chassis number on my 1928 Chummy, I had been looking in the wrong place!
They are quite small characters stamped just forward of the front engine mount and were barely visible under the paint. I scraped off the paint to make them more legible but this actually made them worse.
Does anyone have a cunning plan to make them more visible?

G'day Brian,
I am not sure of the details, but apparently the constabulary use a mild acid etch to show up chassis numbers that have been ground off. Something to do with the metal being compressed to a higher density under the punch. It might be worth a try or further investigation.

I also have a chassis of the same era and haven't been able to find a number either. Can you please elaborate exactly where you found it? Which side? etc and I will have a closer look.

Cheers,
DG

Thanks for the info Dennis, I'll look into that one. The earlier chassis numbers were stamped into the chassis on the left or nearside (for a right hand drive car)just in front of the front engine mount. A good guide to various identity numbers can be found on the A7 Assoc site at www.a7ca.org/Registers/Quote this number.pdf