Does it look like either of these?
They were both made by Smith & Wall in Birmingham, the one on the left in around 1920 and the one on the right around 1930. They both have brass spindle nuts on the back, and are worth around 330 - £50.
If the back looks more like this:
Then you've probably got one made by Walter Dingley and it's worth quite a bit more. I'm afraid I haven't got a photo of the front on a Dingley Centre Brake. Have a look inside and see if there's a "D" stamped anywhere.
And post the photos so we can all have a look.
Regards,
Doc