The makers name on your piece is that of Victor Block, Arthur Danziger Isaacs t/a Danziger & Isaacs. They were Jewellery importers and importers of Jewellery materials. They traded from 9, Vyse Street, Birmingham and also from 26-27 & 84 Hatton Garden, London EC.
The "F" was used from 1867-1904 on foreign pieces imported into Britain. Your piece was made outside of the U.K. and imported by Danziger & Isaacs and assayed in Birmingham.