Thanks for those links. I had previously experimented by setting config.allowedContent to false, which made no difference. However reading those articles through carefully, can see now how that is used.
Removing the config.allowedContent = true setting altogether from config.js works as expected HOWEVER it only applies to formatting relating to buttons available on the specific WYSIWYG area. eg, if the toolbar set for the editable text area where you are pasting (ie, ctrl-v on a PC keyboard) is either the standard or full toolbar, then content coming from Word where there are different fonts, sizes, colours, or tables etc remain in the pasted content. If you change the toolbar on the text area to be, say, the Basic toolbar, then the content is pasted in correctly - WITHOUT any of the superflous formatting!
But that defeats the purpose of content editors being able to apply specific styling to content they create by using the toolbar buttons.
Interestingly, though, if you paste with the keyboard (ctrl-v) in Internet Explorer, all additional formatting is stripped out - ie, you get the same functionality as if you had clicked the Paste as Plain Text button. That is, actually, what I've been trying to achieve, but using other browsers.