Just to close this thread for any folk looking for advice in future I eventually went with Digital-Zones.com.
Just under £30 for the full Home and Business version of Office 2021.
As promised download link arrived less than an hour after paying. Straight to Microsoft official site to retrieve the installer & software package.
Hardest bit was sorting out the activation process. Procedure isn't that clear if you don't instinctively do it the right way.
Doesn't help that it all looks to be setting up the Microsoft 365 online version until they very last page where a magic "Click here if you have bought Office" button appears.Whereupon all is ready to go.
Hate this modern one screen per task approach apparently optimised for old style small scree smartphones. If it were all on one page it would be obvious what was going on.
The one screen per task approach always seems to be an open invitation to error, or near fraud in the case of less honest vendors, as lacking a visible map you have to trust that the succession of clicks isn't leading you astray like a GPS fixated on farm tracks.
Old school notepad and pen to write down the steps is probably a good idea.
Clive