This is most likely an alnage cloth seal of George I. The 1 1/2 signifying the alnage tax paid on the cloth it was attached to. See similar No.184, Fig.28 in Geoff Egan 'Lead Cloth Seals & Related Items in the British Museum'. Here however the 1 1/2 is shown below the crown.
*A picture of the reverse of this disc would help to resolve this if it showed signs of a rivet projection.