There is some confusion here - there was not ever a Mk.3 called simply 'The Club'. Before the advent of the Mk.3 Supertarget proper, the rifle was, during the 1950's, advertised as being available as a 'Target Model', which was basically the .177 calibre rifle fitted with the earlier Parker Hale 16M aperture sight.
However, in Webley's "Export Trade Price List", dated May 1963, there is listed therein the "Super Match Club Model .177 with PH 17B Six hole Aperture Sight and FS 22A Tunnel Foresight", at a price of £16 14 0.
I think this was just one marketing man's description of the gun at that time before the 'Supertarget' name was thought of a short time later.
The word 'Club' is also used in Webley's advertising as a reference to the use of the Mk.3 in the .177 calibre, which is perhaps another way in which the term has been coined as being an actual name given to the MK.3.
Reference my book mentioned, I was told today by a third party, ie not directly from the publisher, that the due date is the 31st July, at a price of £49.99 - I know, I know, I can't understand how they can do it so cheaply! If it had been up to me it would have been a lot more.
Anyway hope the above helps, if anyone can add anything I should be pleased to see it.