Hi Richard,
Welcome to RootsChat and I hope you continue to enjoy us/it in all our aspects  
 
 
Copyright is a thorny theme, and the Copyright Editors will willingly tell you more, but as I understand it, the problem is 
not in reading an image and passing on the information 
on the image, but in passing on 
other people's transcriptions of the image.
As you so rightly point out, the data and images are Crown Copyright and RootsChat also insist that this fact is mentioned in all relevant postings.
You as a private person are allowed to read the images and copy (transcribe) what you see, 
on the imageA commercial company can also transcribe these images and make lists of the transcribed data (
indexes), which they then sell (CDs, pay-per-view, subscriptions, etc).
These indexes are the 
copyright of that company. If you copy their indexes, then you are violating 
their copyright, and this is what RootsChat is warning about.
However, althought the 
index is company-copyright, the 
image isn't, it is still Crown-Copyright. So if you see the image on a commercial site or on a CD you have bought, you are still allowed to look at the 
image and write down what you see on the 
image, as this is still Crown Copyright, with the aforementioned conditions of use.
In other words, you can make your own transcriptions of an 
image, but 
never, never copy a commercial company's transcriptions (
index) of the image.
Hope this helps, but if you would like more guidance, then you can always ask the Copyright Editor.  
The more people know, why we handle as we do, the less need for us to handle !!
regards,
Bob