Does anyone know what date this case number suggests? 1655003. 310787 Any helpful information is highly appreciated!
Dennison UK made case, you should be able to find the date of manufacture using one of the hallmarks here. Not clear enough in your photo.
This document should help: http://webarchive.nationalarchives....ingcouncil.gov.uk/publications/hallmarks2.pdf It only goes back as far as 1678, but that should cover any UK hallmarks related to watches.