Belgian, Customs Seal, Liège, Image by StuE, Found by Nasher.
Found near Baldock, Hertfordshire, 20mm, 22.6g.
One side has the lion rampant on a crowned shield from the Royal Belgium coat of arms as of 1837 (this is the 'lesser arms' used by the Government) with ROYAUME DE BELGIQUE circling it (this is with the help of similar seals). The other side has No1 with LIÈGE above curving downwards and ENTREPOT below curving upwards.
The word DOUANES which is French and Dutch (satisfying both the main languages of Belgium!) for border control customs is often found around the edge of these thick seals but is not evident on this one.