It's listed in Whittlestone & Ewing, Volume 7 (W&E 7540A1). Unattributed, it is part of a series of medals generally showing the Arms of London (although yours doesn't), and featuring “British Made” somewhere on the medal.
This catalogue (from 2009) listed it as Very Common, and worth £3.00.
To be honest, in the condition shown in the photos, you'd be lucky to get more than £1-2 for it.
Cheers
Simon