This is a London hallmark with the crowned leopard's head assay office mark missing. For a discussion about missing marks see this recent posting thread:
viewtopic.php?t=38384. The date letter "e" shows that the spoon was assayed during the assay year 1820/1821.
The maker is John Harris, who registered this mark as a spoonmaker in February 1820. He is normally known as John Harris IV, being the fourth of that name.
Phil