Cloth Seal, Lamb of God, Image & Found by John GM.
Found on the London Thames foreshore.
Probably a disc from a cloth seal with the rivet section missing. It shows the Lamb of God with the initials I B beneath the pennant that usually is the flag of St. George but in this case shows a floret before the cross. There may be some connection with the Knights Templar but it is also used by others as the symbol of St. John.
From Wikipedia:- "In heraldry, a Lamb of God (or paschal lamb, or agnus Dei) is a lamb passant proper, with a halo or charged with a cross gules, and the dexter forelimb reflexed over a cross staff from which a pennon of St. George (Argent a cross gules) is flotant. The seals of the Masters of the Temple in England: of Aimery de St Maur, 1200, Robert of Sandford, 1241, Richard of Hastings, 1160–85, and William de la More, 1304, showed the agnus Dei."