Hello Paul,
Edinburgh AO at
http://www.incorporationofgoldsmiths.co.uk" onclick="window.open(this.href);return false; gives Robert Morton's dates as 1799-1830 and say he was a jeweller. There is no record of his registering a maker's mark.
Andrew Wilkie's dates are given as 1811-62 and in the notes for him there are three images of marks said to possibly be his. One of them is quite similar to that on the spoon. Importantly also recorded in the notes is the suggestion that Morton retailed Wilkie's work.
Edinburgh AO do not mention a mark registered by Morton and Wilkie together nor Morton with Wotherspoon.
It seems the Sotherby catalogue is simply a recognition that there were two marks on the article for sale being that of Morton and another (AW) they attributed to Wotherspoon. More likely is that the AW mark Sotherby's saw and you have here is Wilkie's.
Regards,
Mike
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