Diana & Graham Stevens wrote:

I would really like to be able to view the files before I waste time downloading them

If your browser already displays an image it is because it has in fact downloaded it, whether it is a thumbnail or the full image. They will reside in a file cache. So you may get more traction with this problematic site by saving them directly then viewing them manually.
You could even try drag and drop...

The files I downloaded in March would not open with Preview, it does not even 'see' the downloaded TIFF files. BUT if I do Save-As in GC and save as a TIFF then Preview can see and open the file!!!

That says to me that it is not likely to be a normal TIFF at all.

I use Ancestry for the 1861-1901 census with no problem, I can view and browse through the images on the Internet and then choose download and an image suitable for printing downloads. I can then ctrl-Click to save it and they open in Preview.

I would use that fact as ammunition against British Origins

Neil suggests Picture Viewer but I only have that in OS 9.

Preview is at least equivalent to Picture Viewer.

I was unsuccessful at accessing any images on this site after trying for 5 mins, it seemed as though there was no free service despite the word free being used!

Let us know a quick way to find an image to try to test (even post me one you have).

Good luck
Paul