This find is one from a small group that came in from George Bates. It’s a hammered silver halfpenny, which is only about 15mm in diameter but it is shown greatly enlarged.
On the obverse there is a pellet to the right of the initial cross and the full legend reads EDWARDVS REX An with annulets as punctuation marks. On the reverse the legend reads CIVI TAS LOn DOn. All this adds up to this halfpenny being a coin of Edward III, which was struck at London during the treaty period (1361-69). In the Standard Catalogue coins of this type are listed as number 2353.
The catalogue price in Fine condition for this Edward III halfpenny is £30 so it could be assumed to be common. In actual fact it is quite scarce. The coin would grade Fair to Fine and I’d set the asking price at £20.