Yeah, multiple Address_Street Field sorted!
Tip: change Font setting for Address_ City to All Caps, then comma then space then Address_Postcode.
For CountryRegion issue. Sort your data within MM to just United Kingdom so then leave out Address_CountryRegion.
I presume I will be able to sort data to Exclude United Kingdom and then add the Address_CountryRegion for non UK addresses. We shall we.

Thought I had the issues sorted, preview look okay. Went to finalise merge to new document and lost all the label table settings!
I see that on choosing labels start up in compatibility mode. So started anew, converted file. Repeated all previous steps to set fields and manage line spacing's.
Except MM didn't find Home_Address_PostCode. Had to use ZipPostCode. Probably need to match Home Postcode to the Zip field?
Everything looking fine in preview. Finalise Merge to new document and suddenly all the line spacings change despite my careful settings, suddenly 8pt are added below to the street field where there are multiple line!
Still cannot get the sheet to print within the Avery Label boxes!!
Is the answer to avoid all MS assistance and just type straight into the Avery Label template??!!

After four days of effort, Ive got there! Thanks a bundle MS for making an easy task to incredibly challenging.
Download the label template direct from Avery. Save and open as a .doc. Convert to a .docx, save and open as new. Start MailMerge, select Labels, find your label type and then CANCEL, this will initiate the MM wizard. Find your Outlook data. I had selected and saved mine in a new folder under the full contact set. Add the Fields as above, Format the Fields as above, check the Preview then Final Merge with Edit to New Document. Make any individual adjustments for line length. Double check, triple check every Printer setting, in the document and every printer setting option as MS will keep setting back to Letter, override paper source and make sure to uncheck Auto adjust sizing for large documents and Normal Size is selected.
Good Luck!