I have been given a round Brass clock which I was told was a ships clock belonging to my great grandfather, it has MAWS & SON as the maker on the dial and 'Deptford' I was wondering whether anyone knows anything about it

I think you mean Mayo & Son. Here is an Antique Clock site that may have this maker on it. Antique Clocks Price Guide - Grandfather Wall and Mantel (http://www.antiqueclockspriceguide.com)