Thanks for everyone's help. I subsequently spent some time conversing with 123reg and they are satisfied that everything is set up correctly and they can see the uploaded files on the ftp site.
I have waited the 48 hours that 123 suggest is necessary for everything to fall into place. I therefore looked for my website today (on a different computer to that which I am using here and on which I have been designing the site). I found that I reached a wordpress page which invites me to set up a new site. I ignored this initially but out of curiosity entered my site name and log in. I was surprised to find that this set up another site but, alarmingly, in the same name as the one which already exists.
I am therefore unsure that the downloaded WP file which now sits on the ftp site correclty identifies my site.
How can I check this please?