Friends - I gave up!
(image from goggles4u.co.uk - really!)
I took the glasses and went to the optician on Tuesday and explained the problems that I was having with the varifocal lenses in the new glasses.
He looked at them. He tweaked things. We talked.
He's going to put the distance lenses in the new frames, and then he will use the existing frames that I am still wearing, and make a pair of "reading" glasses for me.
There was no way that I was spending all that dosh on a pair of glasses which I couldn't use, so something had to be done.
I tried with them really hard, but when I was developing headaches after about two and a half hours, and struggling to see what I was doing when I was working, I knew that in reality, this arrangement was not going to work for me.
I may have to try again in a few years, but for now, I am happy that I have made the right decision. Just looking forward to getting it all straightened out and the new glasses back again!