This is the second hammered silver coin from the group that came in from a detectorist named Terry. The first was a penny, the second is larger and a groat.
The coin was struck at London during the first reign of Henry VI. There are pinecones and mascles on the obverse and reverse, so it is a product of the pinecone mascle coinage of the early 1440s. In the Standard Catalogue groats of this type are listed as number 1874.
The groats of Henry VI most frequently found by detectorists are those of the annulet and the rosette mascle coinage from the Calais mint. London groats of the pinecone mascle coinage are quite scarce, so I would set the minimum prices on this specimen at £125.