The lion passant here is of the form used on London marks between 1739 and 1755.
I would attribute this mark as "probably William Dorrell". We know that Dorrell registered marks as a smallworker in 1736 and 1762. The second of these has a pellet between the letters as on this decanter label but the first mark just has the initials. However it is not at all unlikely that a William Dorrell [W·D] mark might have been in the now missing Smallworkers' Register for 1739-1758. To support this theory the Plate Act of 1738 required all makers to register new marks different to their old ones. This is why new registers were started in 1739.